Don't have write permissions to edit files

I got Whonix set up, and everything in place to be running correctly and I was on cloud nine. The only problem I’m having is that whenever I try to go in and change my index.html files in /var/www/, or really do anything (add new file/folder, save or delete a file) I get the message that I don’t have the right permission to do anything other than open and close the folders and files.

Can anyone help me here?

as per Free Support for Whonix ™

It’s a Debian / Linux general question.