Remove the old door tracks and the laser sensor that keeps the door from closing when an object is beneath it.
How to remove and replace garage door.
Attach a couple of vise clamps to the garage door tracks just below the bearings for the second panel.
If you are converting your garage into living space removing the garage door is one of the first major jobs you will face the open space can be filled with a patio door or you can frame a new wall and add a window if you re replacing an old garage door you ll need to remove the door and the spring assemblies and you can decide whether to keep the old tracks and supports or to replace those.
Disconnect the track from the brackets that allow it to hang from the ceiling.
This will hold the upper part of the door in place when you remove the 2 by 4 inch prop to get at the center bracket of the lower panel.