Well step one would be to either take it to a shop and have them clean it or reinstall Windows. Trying to walk you through cleanup would take a long time, possibly end up with you damaging the system which would require a reinstall anyways or not getting it cleaned up properly.
Step two would be to purchase a reliable EPP (end point protection) software such as
BitDefender
Webroot
ESET
Malware bytes Pro
I don't recommend a free solution because generally if it's free you're the product meaning they tend to syphon your personal data