If you just want to change file permissions, you want to be careful about using -R on chmod since it will change anything, files or folders. If you are doing a relative change (like adding write permission for everyone), you can do this:
sudo chmod -R a+w /var/www
But if you want to use the literal permissions of read/write, you may want to select files versus folders:
sudo find /var/www -type f -exec chmod 666 {} \;
(Which, by the way, for security reasons, I wouldn't recommend either of these.)
Or for folders:
sudo find /var/www -type d -exec chmod 755 {} \;
