Need to Transition Control/Ownership of a Minor (Underage) Account to My Adult Child

I am not sure if this is the right place to ask this, but I am seeking advice on a topic. I opened Roth IRA accounts for both of my kids so that they could begin investing with their summer incomes. My oldest child has turned 18 and has begun working for a living. How do I go about transitioning his Roth IRA account to him and remove myself from it?

Thanks in advance.