File permission in var/www/html/index.html?

I'm running Ubuntu 14.04 and I'm trying 2 get apache2 working. I've just installed apache2 and want to edit var/www/html/index.html however it says I do not have permission to edit or delete. I tried doing sudo chmod 755 index.html and it has given me permissions but the file still doesn't allow me to edit or delete it.