You have to have either windows 7 with SP1 or Windows 8.1 with update 1 installed and activated on the machine that you want to upgrade to. To avoid the wait for the windows 8.1 disks from HP, you can download the install (of windows 8.1) from this site:
http://windows.microsoft.com/en-ZA/windows-8/create-reset-refresh-media
Select the correct version to download and it will use your windows 8 key that is embedded. To get the key from the BIOS use rw-everything (google for instructions on how to use it).
Then,
as long as the windows installation is on the drive you are installing on, in theory (as far as I can tell ) you can boot off the windows 10 iso which checks for a windows 7 sp1 or windows 8.1 installation on the drive, and do a clean install which should activate by itself (based on this article
http://winsupersite.com/windows-10/windows-10-clean-install-using-media-creation-tool#slide-0-field_images-57241).
Tried all that. I have the bios key already using the tool.
Here's what I've tried doing thus far.
Installed windows 8 core. Bios key will not activate
Installed windows 8.1 core. Same issue
Installed windows 8 Pro. Same issue
Installed windows 8.1 Pro. Same issue
All were 64bit. According to HP. My laptop came shipped with 8.1
I have Windows8 pic at the bottom.
If I do a clean(not upgrade) install of windows 10, will it take the bios key without having an activated current windows install. If yes then I will not bother with the recovery media from HP.
Also don't have a CD so will need to boot from flash drive.