If your trying to say make your account tenure older, so you appear as an adult over 18, you can't. The only thing you can do is make a new account for that. But if you mean change the parental control to make them looser on a specific account, simply go to the dashboard, move to setting, and change the parental settings. You will most likely need a passcode in order to change the settings, the same passcode entered which made your "underage" account.
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If your trying to say make your account tenure older, so you appear as an adult over 18, you can't. The only thing you can do is make a new account for that. But if you mean change the parental control to make them looser on a specific account, simply go to the dashboard, move to setting, and change the parental settings. You will most likely need a passcode in order to change the settings, the same passcode entered which made your "underage" account.