Step 1. Raise the vehicle and properly align jack stands underneath vehicle. If you have access to a lift like I do, please use it.
Step 2. Locate the transmission fill and drain plugs as shown in this picture. This picture was taken from the rear of the car facing forward.
Step 3. Use a 3/8" ratchet and remove the drain bolt. About 2-3 quarts will come out, so make sure you use a container that can hold this much.
Step 4. While the fluid is draining, attach a 17mm socket to the end of the ratchet and remove the fill plug.
Step 5. Reinstall drain plug after all the fluid has drained and tighten it down.
Step 6. You can use many different types of pumps to get fluid back into the fill hole. You can pick these up from different parts stores for about $20. I use a Honda speed sensor with a couple hose attachments, and an air drill.
Whatever you use, you need to install 2.4 to 2.5 quarts of 10w-30 or 10w-40 engine oil back into the transmission. You will install oil into the fill hole until oil actually leaks back out of the fill hole, that's when you know it's full. If you're unsure, keep filling it up.
Step 7. When you're absolutely sure the oil in the transmission is full, reinstall the 17mm bolt and you're done.
I personally use a 50/50 mixture between Mobil 10w-30 and GM Synchromesh in my transmission for smoother shifting. You can test out a few different things, but do it at your own risk.