Do a full backup and then an upgrade install. Many will tell you without
thinking that you should always do a clean install. The fallacy of this is
that there is nothing to lose and a lot to gain by trying the upgrade. It
usually works out fine (assuming the machine is clean, malware free, and
stable) and there is no real downside if, for some reason, it doesn't. Then
you simply do the clean install and have lost nothing but a little time.
When it does work out, as is usually the case, you can save many hours of
reinstalling software, reconfiguring settings and preferences, and restoring
data.
