Single Key

Yes. Usually it just involves pushing down on the top of the key and sliding it forward. It should come loose. If it's a black one you will have to remove some white ones first. You may have to take out the whole keyboard, but that's usually not that difficult.
Watch out for the little spring underneath the key, don't lose it and make a note of how it goes back when you replace the key.

This is just for replacing the actual key. If you have a problem with the key not sounding then the problem will be with the conductive rubber contact strip under the keys. Pop this off the circuit board and you will see a series of little black disks. Clean these gently with alcohol and clean the gold contacts on the board also. Then replace the strip.