Once you get the CV shaft out of there, the seal is quite easy to replace. Just pry out the old seal and tap in the new. You have to make sure that you get it started square, but it shouldn't go in all that difficult.
You will just want to make sure that there isn't a groove worn into the CV shaft. If there is, then the new seal may not last as long as you would like. If there is a groove... You either reinstall it and hope for the best, or get a new CV shaft. The other alternative is finding a machine shop that can recondition the sealing surface either by spray welding and machining it back off or by machining it down and installing a sleeve, then remachining to size.