How to change User - Role relationships if User is the Administrator and Role field is not editable?

How to change User - Role relationships if User is the Administrator and Role field is not editable?

I created my own user including Name, Last Name, Alias and Role as Administrator. Now, when I try to change the Role, the field is not editable anymore. 

I can change roles in other user profiles, but not in mine. How can I change that?

Thanks