Three steps:
1. Make a backup image of your hard disk, just in case.
2. Make Windows 10 install disk/stick using Windows Media Creator
3. Clean install of Windows 10 (use your Windows 7 license number)
If step 3 fails:
4. Back to factory conditions using the recovery media.
5. Clean install of Windows 10 (will see the restored Windows as valid for a free upgrade)

Kees