5
There is an FAQ that deals with this exact topic and goes at it step by step. You can move sites back and forth between your development sandbox, your test/staging sandbox, and your production server as well as from ISP to ISP or to your local XAMPP (or similar) setup. Use relative URLs wherever you can, of course. But, if you follow those instructions, you'll be able to move things around a lot (and also you'll want to regularly backup things).