There are many steps to adjusting a spring that closes a door. These steps are slightly different for springs depending on whether they require hex keys or tension levers.
Close the door and secure it before attempting to adjust the spring. If the door has a tension pin inserted into the hinge's side, use needle nose pliers to pull it from the hinge. If the hinge has an opening at the top, insert a 5/32-inch hex key into that opening. If it has a horizontal slot on the hinge's side, insert the tension lever into the opening on the far right of that slot. If using a hex key, rotate it clockwise. If using a tension lever, move it to the left. This will expose the next tension hole in the hinge's side.
Next, insert the tension pin into the hinge's exposed hole without pushing it all the way inside. Finally, remove the hex key or tension lever and check the door. If it is not closing with the amount of force desired, put the hex key or tension lever back into the hinge. Remove the tension pin and expose the next hole by rotating the hinge. Then, re-insert the pin and test the door until satisfied.