how can I remove the top of a desk?

I can't think of any universal way to remove the top from any desk out there. They will all be different but will normally have bolts holding the top, which you access from underneath. May need to remove drawers if any. Hard to offer any specific help without seeing the desk in question.

Perhaps you can post some pictures here, that should help. The posting form here (which opens up when you click "Reply") has a little picture icon in the left bottom corner - press it to upload the pictures.

Just stand it up on its side to easily slide it through the doorway. A furniture dolly makes it real easy, but I've done it on carpet without it...I am kickass though. Or, you'll have to be a contortionist and remove all of the screws from inside the drawer pillars for the top...always "lovely" flat-head screws with those.