Obviously I would check state and local laws, permits, etc.. but I believe you can do the work yourself if you get it inspected.
You CAN NOT do work for others unless you are licensed.
Replacing breakers in electrical panel
http://www.youtube.com/watch?v=oIEWWK4jLC8
There are other things you need to know about like grounding, preventing oxidization of aluminum wires, wire gauges, etc...
I did my homework first including talking with electricians.
That link has a very good video re: changing circuit breakers. Thanks!