If it appears that your skylight is leaking, the culprit is often the roof itself and not the skylight. Sometimes water can get in if you haven’t closed it properly, other times condensation can build up on the inside, dripping down and appearing as leak. Snow and ice can also build up above the skylight, backing up into the shingles and causing a leak.
If your skylight frame or the flashing is not the problem, it may be that it needs to be replaced in order to fix the problem. Skylight replacement is in many ways a lot like replacing a window. The biggest difference beyond its location is that the shingles and flashing that surround the skylight will also need to be removed and replaced to reseal it.