[TYPO3-english] create usename/password for typo3 backend

[typo3 study]

Hello,

I want to know how to create username/password and give it administrator
privilege for typo3 backend.
1. It is not me who installed the typo3, so I do not know the
admin(install) username/password.
2. I can logon cpanel, I can manage typo3 through cpanel.
3. I want to create username/password without breaking the site because the
site is live.

So how could I do this? Thanks.