How should I adjust fenders/mudguards that catch on the tires?
Front Fenders typically mount using a mounting bracket at the fork crown and a couple supporting members from the fender to the fork legs themselves.  Since you are dealing with a bike that was presumably designed to utilize the fenders you have, I would suggest that if the rear of the fender is rubbing, detach the supporting members attached to the fork legs (one on each side) re-position the fork crown bracket such that the rear does not rub... (note it is not too uncommon to have to bend the bracket a bit to get the positioning you need)  Then re-connect the lower supporting members.