Start by cleaning up the surfaces you will be gluing.  We use a small amount of rubbing alcohol to denature any grease that may be present on the gluing surfaces. 

Using the small piece of sandpaper included in your kit, rough up the the faces of the roller wheels, and sand off the small numbers on the servo wheels.  Don't spend a lot of effort on this, just rough them up for better glue adhesion. 

Glue each servo wheel face to the roller wheel.  Don't use so much glue that you seal up the hole for the servo mounting screw or muck up the function of the roller wheels.  One trick to make sure you have the wheel aligned is to hold it up to a bright light and make sure the servo wheel's various circular patterns are concentric in the bore of the wheel. 

Five-minute epoxy is nice as it allows some time for alignment as it sets.  Take a look to make sure your work is still in the place you want it.