hi mate, just loosen the nut off on the clamp so it can be turned, preferably get some one to start the car while you hold the distributor (so it doesnt spin round and damage itself)
Then just turn it (i think its clockwise you want) and you will hear the engine speed up/slow downdont do it too much, just remember tye orginal position, THEN REMEMBER TO DO THE NUT BACK UP PROPERLY ON THE CLAMP!
hope this helps
regards
Chris