sudo adduser <username> www-data
sudo chown -R www-data:www-data /var/www
sudo chmod -R g+rwX /var/www
The user should then be able to edit /var/www/ files without hassle.
The first line adds the user to the www-data group, the second line clears up any files with messed up ownership, and the third makes it so that all users who are members of the www-data group can read and write all files in /var/www.
If you are logged in as
<username> you need to log out and log back in for the group membership to take effect.
Source : http://askubuntu.com/questions/19898/whats-the-simplest-way-to-edit-and-add-files-to-var-www