I get the following message when I ssh into my droplet. I probably won't upgrade but that could be one way to upgrade to 13.10. Personally, I would wait for 'til Digital Ocean provides an image - not sure long it will take them.
Welcome to Ubuntu 13.04 (GNU/Linux 3.8.0-19-generic x86_64)
* Documentation: https://help.ubuntu.com/
New release '13.10' available.
Run 'do-release-upgrade' to upgrade to it.