Hi Robert -
If you bought pre-installed Windows the Product Key for your Home Premium licensed version is on the COA sticker affixed to the machine. This is the key you would use if you clean reinstall using a Home Premium retail installer.
If you only want to run your Recovery Disks or Recovery partition to recover to full Factory Condition, then you don't need this key as it will auto-activate during recovery and start up just as it did when you brought it home.
If you use Anytime Upgrade to unlock Pro Features, the key it wants is an Anytime Upgrade Pro key, although the retail Windows 7 Pro key will work.
If you have decided you don't want Pro, then your options are to run your Recovery Disks or the Recovery Partition from boot, or find a retail Windows 7 installer to clean reinstall using these steps: re-install windows 7
Only if you use the last option to clean reinstall do you need to give the Home Premium Product key during install.
I hope this answers you questions and feel free to ask any others. If you give your make/model computer we can help you do the recovery if needed.