It's a simple job to do, but there are some precautions you must take. First off, you
must disconnect the battery and wait at least 5-minutes before starting removal of the old wheel. This is to be sure that the airbag won't deploy while you're working on it. While you wait, I'd recommend putting a piece of masking tape (with a line drawn on it) on the steering wheel, and a piece on the dashboard. This way, you'll know the exact position the steering wheel is meant to be in when you reinstall it. Make sure that your wheels are perfectly straight before you even start the removal.
The next step is to loosen the two Torx head screws on the back of the steering wheel on each side (they won't come right out, they just become loose). This will allow you to pop the horn pad off and disconnect the airbag and horn connections (just be careful not to pull on the actual wires for the airbag/horn when disconnecting the plugs). Put the horn pad in a safe place, but make sure that the Toyota symbol on the face of it is pointing
upwards.
Once that's done, you can now loosen the center nut on the steering spline. Make sure you only
loosen this at first, as opposed to removing it entirely, as this will stop the steering wheel whacking you in the face when you're pulling on it. With the nut loose, place both hand on each side of the steering wheel and begin to rock it from side to side until the wheel becomes loose. One you've done that then you can remove the center nut completely and slide the steering wheel off the spline.
The installation is the opposite of removal. As long as you've got your battery terminals disconnected and the horn pad with the Toyota symbol facing upwards, you shouldn't have any problems. Be sure to test that your horn works afterwards and that the steering wheel is central when you're driving straight. Best of luck