How to get su priveleges

I am trying to replace the my.cnf file in my MYSQl folder in a unix machine but the file has write-enabled protection. How do I bypass this since I need to make edits to the original file and replace it? I also need to delete file that are write-enabled but I cannot. Is there a way I can perform these tasks?

The 'usual' ways would be to use the same user that mysql was installed as (often mysql), the root user, the su command to 'become' a privileged user (either mysql or root), or sudo to do the same thing as su.
It is best to leave the permissions of the file as they are, generally such files are 'write-protected' for a reason!

To get 'su privileges' you will need to know the password for the user you wil lbe switching to. For sudo (if installed and configured) that may not be needed, depending on what you are authorised to do (in the sudoers config file). Of course, you'll need to be root to update the sudo configuration ...