To remove the pelmet that hides the door rollers, first run a sharp knife along the join between pelmet and door frame to cut the paint. Locate the screws and unscrew pelmet.
To adjust the door, you’ll need the thin offset spanner supplied with the door. (It’s sometimes found in a clip on the top of the door.) If there is no spanner, you’ll need to contact the manufacturer to provide a suitable replacement.
There is a nut that connects the rollers to the plates fixed to the top of the door. Turn this nut to change the height of the door. Check to see that the door is operating smoothly and continue adjusting as necessary.
Return spanner to clip at top of door, put pelmet back in position, and screw in place.