Roger Shoaf wrote:

Look at your door. You probably have a track that is in sections.

Open the door partway so the lower section of the track can be unbolted and
then you can probably flex the door enough to slip out the old one and slip
in the new one.

What you might want to try is when the door is open fully, Close it a
few inches. that sholuld give you enough room to slide the old rubber
bottom seal out and put the new one in. Also, it would be a good idea to
go buy a can of light spray grease and spray the metal track that the
bottom seal slides into. It will make things go more smoothly. Also, it
would be a good idea to get the help of someone else to feed the bottom
seal in while you pull it down the door.