I don't know how amateur you are so it's hard to say whether you can or not. But if you're not too mechanically declined you should give it a go.

The only thing difficult about replacing a canti cable is finding the best length of the yoke (crossover cable) so I suggest measuring yours before you start. Here's a decent tutorial on Park tool's site on canti's with cable instructions within it. If you think you can follow it go ahead. Worst case, you get frustrated and pay a visit to the LBS.

BTW- since brakes are a safety item, if you're at all unsure have a knowledgeable friend check your work. Also, I suggest that if it isn't already that way the front yoke cable be routed over a fender or reflector bracket or just a bolt in the fork, so that if your job fails, the yoke can't be pulled down into the tire locking the front wheel. Yoke retainer devices are mandatory for canti brakes in Europe, but not much thought is given to them in the USA.