When you upgrade from precise . . .
don't forget about reporting your results to the isotracker (including bugs!). During the milestone testing (like alpha 1, alpha 2, etc) bugs reported this way even get extra attention from the applicable developers as during the milestone the archive and iso should be in a stable and working state.
Right now for alpha 1, the links are:
Upgrade i386 ubuntu
Upgrade amd64 ubuntu
And for you flavor folks, there are upgrade tests for you as well! Please report your results good or bad. All you need is a ubuntu SSO account to login.