If necessary, remove the old trim from the door.

Caulking applied to the seam between the door trim and the sheetrock can tear the paper on the sheetrock when prying the trim off. If there is such caulking, it's wise to slide a sharp utility knife along the seam to make a clean cut through the caulk down the full length of the trim before prying.

With a hammer or pry bar, gently but firmly pry the old trim off the wall.

For best results, place a shim between the hammer and the wall to minimize damage.

Start from the corner, and work along the length of the trim.

It is not uncommon for some nails to remain stuck in the frame after the trim is removed. Use a hammer or pliers to remove them.