Yes, you can use retail Pro key to Anytime upgrade from Home Premium.
Type "Anytime" in Start Search box to start the process, insert Pro Key, extra features will be unlocked in minutes.
Quote: Originally Posted by profdlp
It can be done, but you may need a registry hack to make it work. Basically you go into the registry where the OS is listed as "Home Premium", edit it to say "Professional", then do a repair install.
This workaround is how an in-place Upgrade or Repair Install
from HP to Pro can be done from the HP desktop, but this isn't necessary because Anytime Upgrade will allow use of a Pro Retail Key which simply unlocks the extra Pro features in the HP install you have now.