I have forgotten my admin password.

What about your OS X version?

For higher version of OS X, If FileVault is disabled, you can try to reset your admin password using your Apple ID. That's the easiest way for everyone. If you have set a master password, you can also use it to reset your admin password. Additionally, you can also try to create another admin account to reset your current account. You can also reset your password in Recovery HD.

An iMac cannot run iOS, and this forum is for very old versions of OS X.

What version of OS X are you running?