Cannot update Ubuntu 12.04 to 14.04 in DigitalOcean

I recently faced the problem of not being able to update Ubuntu 12.04 to 14.04 in my DigitalOcean droplet.

Despite these great instructions:

It did not work because there were missing files.

I had to manually edit the sources list

sudo nano /etc/apt/sources.list

And uncomment the original DEB package sources, and comment the Digital Ocean mirror packages.

Hope it helps!