If you want to downgrade from 8 to 7, you CAN do it, you just need to purchase Windows 7 and a license for Windows 7. Do a clean install of 7, Format the drive Etc... Considering it's an older machine, you may have issues running windows 10, as there are many drivers from the XP era that will not have compatible drivers in Windows 10. Windows 10 may be an even worse option than 8 considering the age of the machine.