If the key is not broken, just "sticky" or malfunctioning, procced up to this step. You can now wiggle the white silicon portion of the key's interior around, pushing down on the extended part of the silicon and wiggling it back and forth. Once you have done that, you can replace the key as described above.

Furthermore, you can remove any debris from under the keys at this time with a toothpick or a dampened q-tip, which may improve the performance of your keys.