Open your door so that you have access to the hinges. Look at the top segment of the hinge and you will see the adjustment capstan.
Remove the tension pin from the hole in which it fits in the side of the adjustment capstan. Insert the end of a hexagonal wrench into hexagonal port in the top of the capstan.
Turn the wrench counterclockwise to loosen the tension on the hinge. Remove the wrench from the capstan. Insert the tension pin in the hole in the side of the capstan.
Shut the door and open it. Determine if the tension is at the desired strength. If it isn't, remove the tension pin, reinsert the wrench and loosen the tension some more. Reinsert the pin and test the door again. Repeat one more time if necessary. You can also increase tension if need be by turning the wrench clockwise.