Remove the old trim with a utility knife and pry bar
Score the caulk line to prevent wall damage
Pull off the casing carefully
Remove any leftover nails from the jamb and wall
Measure the door frame sides and top
Cut new trim pieces to size with mitered corners if needed
Dry-fit the trim around the door
Apply construction adhesive or caulk if desired
Nail the trim into the jamb and wall studs
Countersink nail heads slightly
Fill nail holes and gaps with wood filler or caulk
Sand the filled areas smooth after drying
Prime and paint or stain the new trim