Be sure to scroll down... there may be more than one question on this page!
First, enlist the aid of a strong friend! Offer food... whatever it takes!!
You can remove the garage door opener first or remove the door first... whichever floats your boat. Let's assume you want to take the opener down first.
Disconnect the opener from the door by removing the control arm from both opener and door. Lower the door, unplug the opener and disconnect any wires. Unbolt the opener body from the ceiling brackets and let it pivot down to the floor. Disconnect the garage door opener track from the bracket above the door. Throw the opener in the woods (only kidding) so it's out of the way.
Raise the door, pushing it up as far as it will go... right to the stops! Put C-clamps on both tracks to hold in this position. Disconnect all springs and cables. Be careful... even with the door up there may be some minimal tension in the springs.
Starting with the topmost panel, remove all hinges between the doors so that the door panels swing downward from the rollers and hang on the track. Let it hang down. Repeat with remaining panels.
Now remove the clamps that you put on the tracks. Slide the panels down, one at a time to the ground. Disconnect the roller brackets to free up the panels from the track.
Good luck, and be careful!