You can probably effect a clockwise roll of the door in the frame by adjusting the roller on the bottom opposite the affected area. Look at the bottom of the door. There should be a hole (possibly plugged) into which you can insert a phillips screw driver and increase or decrease the height of the roller. Increasing the height will cause the door to tilt toward the top where you have the gap. Let us know how that goes.

Hi there, Typical off the shelf prehung door will be set up with 4 9/16 jamb for stud plus 1/2 drywall as Mitch said. Sounds like you might have an adjustable jamb that slides together from both sides of opening. Same question from me...What size gap do you see?

Standard wall thickness is 4 9/16 (2x4 + 1/2 drywall on both sides). So you will probably want to add a thin extension jamb onto one side of your jamb. Usually the side of the jamb that does not have the hinges and latch is the best side to put it on. You usually want to leave a 1/4 reveal, or step back, when you attach the extension onto the jamb.