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Assuming your are the owner and administrator of said PC, go to Control Panel, User Accounts, click Change account type, and click Administrator.
You might find the tutorial more helpful (and clearer) - How to Change Account Type of Users in Windows 10
If you are not the owner or administrator you'll have to contact the actual administrator for those permissions.
The very first account that is created is automatically a member of the 'Administrators' group, i.e. not THE Administrator (which is disabled by default) but pretty close.