It depends on how confident you are with your sewing, and how experienced you are. Altering pants *can* be tricky. It's much easier to do with pants that don't have a waistband, or have an elastic waistband. If your pants do have a waistband, you'll either need to remove it entirely, or seam it in the back.
The nice thing about pants is you have a lot of seams to work with, so you can get a good fit!
I'd recommend checking out one of the Singer Sewing Reference books (they have one on making pants, which may help) or the Readers Digest guide to sewing ... I recommend that one as a wonderful sewing "bible" for anyone.
The process varies so much by how the pants are constructed that it's hard to explain in a couple paragraphs. Hopefully one of the books above will help.

Good luck!