Failed Hackintosh, how to turn into a regular PC again?

Hello, a couple of years ago an acquaintance of mine built me a Hackintosh PC that came with both windows 7 and OS X installed.

I never use the OS X because it freezes and messes up the time and date every time I log in.

I've been using Windows 7 all this time and now I want to upgrade to windows 10 But haven't been able to uninstall OS X, I really don't know how.

My PC boots up with a Mac startup with some icons and I have to choose the one with windows every time.

What is the best way to uninstall it?

Thanks in advance