Not sure if this is answer but might help.
Often adjustment systems have screws designed into the system for this very purpose - see your kitchen cupboard door. Adjustment is very suttle and complete door adjustment will probably depend upon adjusting both of these screws. In doing so you may have to keep going backwards and forwards between them.
Sit down and work out how the door needs to move to solve the problem and then try to identify how this could be done.
Initially try gently lifting the door at the handle side to see if any hinge screws might already be loose.
These are only life-lines - I don't otherwise know.
With wooden doors it might have involved packing beind one or both hinges but with upvc it's going to be more suttle.
Nyge, March 2011
