|If you want to upgrade to Windows 7 there is no need (and no point) in doing a factory reset. Just buy a Windows 7 upgrade DVD, but as guapo says, back up your existing data first.|
Lenovo do have Windows 7 drivers for that model:
Be aware that you may have a problem finding Windows 7 in the computer stores now that Windows 8 has been on the shelves for some months. Microsoft reclaimed all the unsold copies of Windows 7 worldwide. Buying it online will probably be the best option (and usually cheaper too). Try Amazon.