Accidentally changed user from Administrator to Standard. How to fix?

I went into users & groups to change the name of my account/user name and not only was that not successful but the account changed from administrator to standard and there is no administrator account now and when I try click the gold lock button at the bottom it asks for an administrators name and password and when I enter the information it doesn't work because I guess now there is no administrator. How can I fix this? I've been trying to fix it and haven't been able to. Any suggestions? Thank you.