If I completely erase memory from my " h p Windows 10, touch screen lap top, it says it will go back to a " windows 7."!?

I have a. h p Windows 10, touch screen lap top, I really need to completely ERASE the memory . It says that if I do it will go back to Windows 7. HOW do I get it Back to a windows 10 after it gets loaded back up ???? I was told I would have to use the ( Product key ). Where is it and what do I do ??? Please... show more I have a. h p Windows 10, touch screen lap top, I really need to completely ERASE the memory . It says that if I do it will go back to Windows 7. HOW do I get it Back to a windows 10 after it gets loaded back up ???? I was told I would have to use the ( Product key ). Where is it and what do I do ??? Please help. And will it cost me to load all the stuff back in it and get it up and running ???? Please help. And Thank You.
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