I do that all the time. Removing the door is fairly easy. Just reverse the installation process. One thing that you may run into is that often, expanding foam insulation will have been used on the sides and top of the door. This glues the door into place and you have to cut the foam to release the door. It is easy to cut with a sawzall blade and, in addition, will help you to find any screws or nails that you missed.
When the sides and top are loose, you may find that the sill is glued to the concrete and if you just try to pull it up, it will bend and become junk. Be careful at this point to cut or pry gently under the sill until it comes loose. This is where the sawzall will come in handy again. If you can get a long blade under the sill, you can cut the adhesive loose and the door will rotate out of the opening (make sure you have someone holding the door).
Clean all the old foam, caulk, or adhesive off of the floor and the door, then reinstall correctly.
I have done four of these exact jobs in a day with just a helper.