How to log in in FTP

Hello,

We have chosen an theme for our website, but we would like to change some things. We read that you should log in to FTP to change that. Our domain host should know our FTP credentials, so we called them. But they told us that our domain is placed at wordpress itself, so they couldn’t give us the credentials.

Can anyone here tell me how we can get the FTP credentials and were I should log in?

The page I need help with: [log in to see the link]