How do I cleanse the focal points?

In order to purify each one, you have to equip the Mystic Tuning Gloves and then go around to each focus point to activate them.

There are 3 focus points in total, they are located in:

• Hall of Countenance
• Main Courtyard
• Hall of Attainment

http://www.uesp.net/wiki/Skyrim:Out_of_Balance

If you approach Drevis Neloren in the Hall of Countenance at the College of Winterhold, you are able to ask him if there is any College business that you can assist with. He will then say, "There may be a matter in which your... skills... could be useful. The various points of focus for magic energies around the College have become polluted, and need cleansing. The magical energies underneath the college still require purification. Your assistance would be most useful." Choosing to agree to help, Drevis will further elaborate on what has to be done: "Very well. These specially enchanted gloves will allow you to delve directly into the focal points for these energies. Go to each focal point and remove whatever impurities you may find there. Return the gloves to me when you have finished. Please exercise caution. This is not a procedure without possible... consequences." If you ask Drevis to repeat what has to be done, he will say, "Use the gloves to clear the focal points. Return to me when you have finished. I thought I made this rather clear."