On the RX end, yes, you can just change crystals. Some Futaba RXs have "high band" and "low band" on them for the top half and bottom half of the channels. If your RX says that, you'll want to stay on that end of the channels.

On the TX end, if your radio has a large module that comes out, then you can change channels easily by replacing the whole module. However, if all you have is a crystal that can be removed then bassmanh is correct, you shouldn't just change the crystal. (I'm not familiar with your particular TX, and I'm too lazy to go look it up ) In fact, I am under the impression that it is a violation of the FCC rules and if something went wrong you can be pretty sure any insurance (AMA, or whatever) would try to use it as a reason not to cover you. However, a lot of guys do change channels by a channel or two with no problems, since the tuning differences would be small. You shouldn't do it, but it has been done many times.

In general, you are almost always best off with small changes anyway.