There are those who would call that an upgrade. 😀 Unfortunately, it will cost you for a licenced copy of Windows 7.
If you really want to do it, download an ISO of the version you want from the Microsoft website and burn it to a CD or USB device then install it. When it comes to activation time, Microsoft will sell you a licence but it won't be any cheaper because it's now a nine year old system.
You might like to go to our Windows 10 sub-forum and ask for some advice on the problems you're having with 10. You'll save a lot of money.
Ignore any post that follows this one saying how you can get one for nothing or very cheap - they rarely work and the crooks who sell them should be in prison.