I had a similar issue some time ago: no information was obtainable online, I ended up going trough WRI's user portal. There is a support portal there that I used. I described my problem in the greatest detail and after a few working days I got a response. The email conversation which followed ended up with them giving me a new license that I could use on my new system.*
For buying, you can just go here and select the home edition. You also have the option for upgrading from a previous version.
*My system was the same but with a new OS, Win 8, and a new SSD.
I think the home edition license is limited to use on one computer.