Crisps, on 06 May 2012 - 02:19, said:
Externally back-up all your data. Then do a fresh clean format / install.
Or install to a different partition/drive (different drive by preference).
Yes - you CAN do a clean install from upgrade media (this has been possible since 9x/NT); all that is required is that a qualifying product be accessible during the installation (first stage or second stage - for NT-based Windows, it's the second stage).
Also, you can import (via Files and Settings Transfer) from x32 to x64 - I have, in fact, done so.
Still, a clean install *is* preferable (of the old applications, if you want to still use them).
Suggestion/tip - if an x64 version of an application is available, use that instead (unless constrained by plug-ins or add-ons for the application in question); I crossgraded from Firefox to Waterfox and (thanks to having already installed the x64 versions of my plug-ins), I basically hit the ground running. NOTE - GreaseMonkey (and scripts developed for it) *are* compatible with Waterfox.