How do you promote your account on xbox one

It should automatically promote the account once it comes of age. Remember that changing your birthdate on account.microsoft.com will not carry over to your Xbox account if at any point that was done.

You will have to promote your local account to a Live one. This will require a new email address that is not already linked to a Live account.

If you want to use the one that is tied to your current Live account, then you will need to change that one to a different email address which will free the old one up to be used when promoting your local Profile. Information on how to do that can be found
here
http://support.xbox.com/en-gb/xbox-live/how-to/xbox-live-account-management/manage-live-id.

It's possible that the account belongs to one of your parents, but the gamertag is just one you don't recognize. They may have gotten a forced name change, etc. Have them try to sign in and see what happens. You can also try to promote your child to adult
status. Here's how to do it on Xbox One: http://support.xbox.com/xbox-one/security/promote-child-account?lc=1033

I am pretty sure you must do it on your console, but you know how things with Xbox change daily! LOL Can you try and do it on your console? It should be under account management somewhere and it'll say "promote account" if your account is promotable.

I can see how that would be a problem with certain games and content, unfortunately there's really no way around the limit unless you created a new LIVE account but then you'd lose all the content that you have on your current tag like achievements, saves,
dlc etc.