Why would you need to alter the crossover frequency? This does not seem like a feasible move to me... The frequency the sub crosses over at should be the lowest frequency your satellite bass drivers can go to in the real world, otherwise you will be left with a frequency gap. The only time you would need to lower the crossover frequency of your is if you use larger satellites with a lower base frequency. Chances are, if that was bought as a system, it was designed to work with the satellites it came with, and the set frequency is matched for the whole system. Looking at the photo, the satellites don't look like they would be capable of going as down to 100Hz in the real world (not just on paper) - many speakers claim to have a bottom frequency of 60Hz, but in reality a 6" cone could not physically move enough air in the room to be heard from any distance, which is where the sub comes in.
If it sounds wrong in your room, and you are getting boosted or dropped frequencies, then look at the modes of your room, and speaker placement (there are many online room mode calculators available online for free), you need to read up on room acoustics and look at speaker placement, rather than changing frequencies set at the factory which were matched for that system as a whole. Chances are it's standing waves and the resonant frequency of your room which is more the problem than the actual speakers, which could better be solved with a few bass traps in the corners and a reflection free zone (RFZ) opposite your satellites..
I have set up a number of recording studios over the years, both commercially as well as repairing faults in existing setups. The amount of times I've gone into a home studio where the owner has spent thousands going through several speakers and getting the same results with boosted frequencies by placing them direct onto their computer desk causing early reflections from the desk itself. This isn't limited to recording environments, basically anywhere you have a speaker system.
Read more about acoustics, and understand what might be causing your frequency issue here:
http://www.indiana.edu/~emusic/acoustics/reverb.htm