How to upgrade 1511 from Home to Pro?

I'm not having any luck figuring out how to upgrade from Home to Pro with an existing key.  My system has been running Home and is currently running version 1511.  I've decided to go ahead and use an existing key to upgrade to Pro.  I did a clean install, expecting to be asked to specify a version and provide a key during install, but was never asked for either.  The installer simply formatted the hard drive and installed Home and activated it, with no input from me after the install started other than agree to the terms and tell it my language.

OK, no problem I thought, I'll just go to the Activation setting and give it the new key from there.  However, if I tell it I want to change the key it comes back and says the key I'm giving it can only activate Pro and I'm running Home.  If I go the Store route and tell it I already have a Pro key, it gives me the same message - it tells me my key is for Pro but I'm running Home.  Nowhere along the way does it offer to take my key and give me the upgrade, rather it implies that I must somehow magically upgrade it myself before changing the key.  And that would be fine if I could figure out how to do that.

Anyone know how to force an install of Pro when the installer automatically installs Home with no option given to change it?

windows pro

Did it work?

There is no guarantee that using the old key to activate is still turned on.  But we would probably have heard here if it was turned off after the grace period that was being allowed, so it may be worth a try.  If it will no longer work you can still always open the Contact Support app to ask for an Exception from MS Support.

When you upgraded to Windows 10 Home the PC was assigned a permanent Digital License in MS Servers to Clean Install Windows 10 as often as you want.  You presently have a Home License.  If you add a Pro Digital License it will be stacked along with Home on the PC so you can reactivate either.  You can associate these with your MS Account in Activation settings at any time by signing in with your MS Account.

Save a System Image backup of Windows 10 using Macrium Reflect is a Free and Easy To Use Backup Utility to use in place of reinstall in 20 minutes.  Macrium offers more flexibility for where you can restore than Windows imaging. 

Then you can try directly inserting the Windows 7 Pro key in Activation Settings link to Change Product Key.  If this fails insert the Windows 10 Pro default Product Key  VK7JG-NPHTM-C97JM-9MPGT-3V66T  which will change the version to Pro.  Afterwards you can attempt to insert the Windows 7 Product Key to activate.  If this fails I would open the Contact Support app to ask for help activating, if necessary asking for an exception. 

Another way you can do this while keeping the present install intact is to Shrink C in Disk Management to Clean Install Windows 10 Pro to the shrink space to attempt to activate with the Windows 7 key.  Iif it fails open Contact Support app to ask for help or an Exception.  If that fails you can delete the new install and Extend C back over it.  You could also use Macrium to clone Home to the shrink space, change it to Pro using the Default key, then attempt to activate.   Cloning a disk

If the test install does activate Pro when you're ready to get rid of Home you can delete its partition and recover the space to the left using Partition Wizard to Resize Partition - Video Help.

Feel free to ask back any questions and let us know how it goes.

Sorry for resurrecting this old thread.

I have an old Win 7 PRO key that I just found on a bottom of a shelf.

My system has Win 10 Home and I want to try this method.

Questions:

1. is this method still available or was it for the free update period only?
2. how do I go back to Home if something goes wrong for some reason? The system has UEFI Bios and for that I never had a key in my hand for the Home edition in order to manually change it back.

Thanks