How to perform a clean Windows 7 Upgrade.
1. Purchase Windows 7 Upgrade in the retail package. Your existing computer must have Windows XP or Vista on it.
2. Backup your data to an external harddrive, to a flashdrive, to a dvd, to a NAS, to the cloud, etc.
3. Put Windows 7 Upgrade disc in the computer. Use the 64-bit disc if your computer hardware supports 64-bit.
4. Perform clean install where you format the harddrive. DO NOT CLICK UPGRADE.
5. Follow through the install. When it asks for a license key, DO NOT ENTER THE LICENSE KEY. Click skip.
6. Finish with the install and you should be at the Windows 7 desktop.
7. Go to Computer then your optical drive, D: or whatever it is.
8. Run the Windows 7 Upgrade install. This time select Upgrade.
9. If it asks for a license code, provide the code.
10. Complete the install.
11. Check if your computer is activated by right clicking on Computer and selecting Properties. It should say activated. If not, activate the computer and if necessary enter the key.
12. Your computer has Windows 7 cleanly installed without any junk or old files from the previous OS.