Help removing 81-257?

I'm sorry to hear that you're having trouble. Is this an older aluminum door? If so then it's very likely that your door has a bottom rail that has to be removed first. This rail runs along the entire bottom length of the door and is affixed in place pretty firmly. Once you remove the screw at the bottom corner of the frame, you need to use a mallet and a block of wood to gently tap the rail off. That should allow you to remove the roller without any issues.

Just be sure to use a light touch with this. You don't want to accidentally smash the glass. If you have any doubts then you may want to contact a local professional to come out and do the replacement for you.