It's kinda hard for one to answer this question when one is not familiar with your web site configuration.
Given that he is actually talking about a directory path 'cgi-bin/cache', you'll have to login to FTP to modify files there. You would want to look for a directory named "cgi-bin" and inside it would be a directory named "cache".
In Windows XP, you may be able to access it by browsing to ftp://hostname/ where 'hostname' would be 'ftp.[your domain]', eg 'ftp.example.com'. It will prompt you for your FTP username and password.
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