How did you upgrade to Ultimate from Home Premium? If you bought Upgrade version of Ultimate you can use it to clean reinstall, however if you bought an Anytime Upgrade key then you'll need to reinstall Home Premium first and then run Anytime Upgrade.
Follow these step to Clean Reinstall - Factory OEM Windows 7
. The steps are the same for retail.
Remove the EFI BIOS boot disk from BIOS Boot order if it appears, then wipe the HD first before reinstall with Diskpart Clean Command
from installer Command Line accessed by Shift +F10 at first screen. After the Clean command completes, type Convert MBR, then Exit. Close box and begin Install.
I assume you had specific features you needed in Ultimate to decide to spend all that money on the same OS with just a few extra features that most users don't need? Compare Windows - Microsoft Windows