Changing the transmission fluid in your vehicle may not be such a difficult thing, but what you may find difficult is making sure that you change the whole system over. You see, simply draining the oil from the pan and refilling it is not enough, at least if you're switching fluid types.
If you're going to switch to synthetic, you want to make sure you're getting the most bang for your buck. Thus, you'll want to make sure that you get as much of the old fluid OUT as you can so that you can put as much of the new fluid IN as you can.
The problem is that your torque converter will be holding some fluid which won't be pushed through unless the vehicle is running. You need to somehow get that fluid out. You can take it to a shop that can do a complete transmission flush and refill, but they'll charge you an arm and a leg to do it.
Here's a way that you can do it yourself without doing any damage to your transmission and without removing the torque converter. You'll need at least two and maybe three people to do the job, but not because it's that difficult. You just can't be in more than one place at one time.
Here's the plan. Find out how much fluid your transmission holds. Then find out how much fluid your torque converter holds. You may have to contact your local auto dealer for that info. Add the two together and then add about two quarts to that total. You'll probably need the extra to do the job, but if you don't at least you'll have some extra for topping off if it ever becomes necessary.
Now, change the fluid in the transmission fluid pan and replace the seal and the pan. Once the pan has been replaced, you must refill it with fresh ATF. Pour in as much ATF fluid as your transmission holds - that's typically the number listed in your owner's manual. Once you've topped off the system with new ATF, you're ready to flush the torque converter.
There are going to be two lines which run from your transmission to a cooling system of some sort at the front of your vehicle. This will either be a special section on the bottom of your radiator or a separate transmission fluid cooler. It shouldn't be that difficult to find.
Disconnect one of those two lines. If this line is flexible, then disconnect the end that attaches to your transmission (making sure to clean any dirt off the end of the hose and the area around the connection first). You'll use this disconnected end to drain fluid from. Don't disconnect the other end.
If it is not flexible, you'll probably need to have some extra temporary, flexible hose on hand to use. In this case you'll disconnect the same line, but disconnect it where it comes out of the cooling system, NOT where it attaches to the transmission (again making sure to clean the area around the connection first). Then connect one end of the flexible line (brake line should work - ask your local auto parts store) to the fluid cooler (where you removed the other line) and leave the other end unconnected to drain into a pan.
No matter which way you have to do this, keep in mind that although there might be a small amount of drainage when you first disconnect the hose, it should be minimal and should stop quickly (far less than a half quart). The hose will not drain again until you start the vehicle. If you're not sure you're following, don't worry. It will all become clear.
Now, this is the part where having two people will come in handy. You want to have one person in the vehicle turning it on and off. The other person will be at the front of the vehicle taking care of the draining and filling of the fluid. First comes a little draining.
Have the person up front hold an empty ATF quart bottle with the fluid drain hose in the mouth of the bottle. It will be easiest if the ATF bottle is clear, but it doesn't have to be. As long as you have some way of seeing the fluid level as it rises (you don't want to overfill the bottle and have fluid run all over your hands).
Once someone is in place with the "drain hose" pointed into the "drain bottle", start the vehicle. When the bottle is about full, the person holding the bottle needs to yell to the person in the driver's seat to shut off the vehicle. Once the vehicle is shut off, the hose will stop draining.
Now, you know that one quart of old ATF has been drained. So, have the person at the front of the vehicle, pour one quart of new ATF into the transmission fluid fill tube. Then, you're going to repeat the process. Put an empty quart bottle under the drain tube, have the other person start the car and run it until you fill the bottle again. Once the bottle is full of old ATF, shut off the vehicle and pour in another quart of new ATF.
This process is going to continue until you see a definite color change in the fluid draining from the hose. In other words, what you're looking for is the drain fluid should eventually look exactly the same color as the new ATF you're putting in. When it does, that means you've got the entire system flushed. At that point, you can stop, reconnect the hose and take the vehicle off the ramps. Then, you simply need to check and make sure that you're ATF fluid level is up where it needs to be (and it should be pretty close).
A note about the color change. I suggest that you use the following method to establish when the system has been completely flushed. It MAY be difficult to watch the fluid being drained from the hose and see the color change if the old fluid isn't really that old. So, to make sure you know when it's been flushed, get yourself two clear shallow containers, like tupperware or the bottoms off a couple of milk jugs or something.
Each time you fill a bottle with old ATF from the drain hose, pour just a bit of it in the bottom of one of those containers. In the bottom of the other container have a small amount of the new ATF. Compare the two. If the colors do not match exactly, your system has not been completely flushed. Dump the old ATF out of the one "comparison container" back into your drain pan and try again. When the colors match exactly, you know that you're done.