FTP Credentials??

I am trying to upload a new theme and I am receiving this message: “To perform the requested action, WordPress needs to access your web server. Please enter your FTP credentials to proceed. If you do not remember your credentials, you should contact your web host.”

I have tried a few different things but I really have no idea what this information is. I don’t know what my hostname should be and I am not sure where I find my FTP username and password.

Help!