[TYPO3-typo3org] old website - new in TYPO3 - please help

[giovanni razvan]

INTRO INFO: 
i have an old website administered by somebody...  we will not colaborate anymore now. 
i wanted to edit the website and i discovered that was done with TYPO3 ( as i saw some files in the server FTP) 

MY PROBLEM: 
i do not have any idea how to edit the website now... what i have to install?  on my computer?  how can i access TYPO3 interface to edit website? 
any help is very precious as i have to update website info

THANK YOU in advance