Measure the existing door, frame, and rough opening
Remove the old door slab from the hinges
Remove the interior and exterior trim
Cut any caulk or paint sealing the frame
Remove the old door frame and jambs
Inspect the rough opening for damage or rot
Repair or replace damaged framing
Check that the opening is level, plumb, and square
Dry-fit the new prehung door in the opening
Add flashing tape and sill pan if needed
Apply exterior-grade caulk to the threshold and rough opening
Set the new door frame into the opening
Shim the frame at hinge points and latch points
Check the door for even gaps and proper swing
Fasten the frame securely through the shims
Recheck that the door opens and closes smoothly
Install insulation around the frame gaps
Reinstall or replace interior and exterior trim
Caulk around the exterior trim
Install the lockset, deadbolt, and strike plates
Paint or stain the door and trim if needed
Test the door for alignment, sealing, and locking function