How long it has been since you upgrade to Windows 10?
If it has been 10 days or less, then you may open start and go to Settings and then click on Update & Security and click on Recovery and you should see option to Go back to Windows 7. In case, you don't see this option or it is disable, then you couldn't downgrade to Windows 7.
You need to perform a Clean Install and reinstall Windows 7.
Your files and data will be placed in a folder called Windows.old but you have to reinstall you applications and make sure you have their products key ready (if any).