I hate to link to other forums, but Roland has an excellent guide with video and links to everything... all in one post and better than mine. Check it out:
How to install jcsullins CyanogenMod10 Preview 4 with Sound, Updated 11/16/2012 - HP Touchpad - RootzWiki
This does not mean I'm recommending installing CM10 for everyone.
CM10 is a preview for a reason, in that there are risks associated with it (like potential bricking) and should be left only to those who know how to fix an unbootable device.
Still the procedure is the same for installing CM9 or CM10 or updating to a newer version of the same rom you have now.
Make sure you get the correct downloads for the rom you hope to install since installing a version of gApps that doesn't match your rom, could be nasty.