In Control Panel, go to User Accounts. To quickly get to Control Panel, click the start button and start typing 'cpanel'.
Select your user name, and there should be a link to the left of your user image that says Change Your Account Type. This is where you can change to Administrator.
BTW, your version of Win10, did you upgrade from Windows 7, by chance? There are documented issues with file ownership, coming from a Win7 environment.
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