Hey friend,
Great question! I think there’s a lot of room for disagreement with my answer, but my answer is my opinion on the subject. In my honest opinion, spin up a new droplet and migrate Wordpress to it. When finished, swap your DNS to the new IP and call it done. For most Wordpress sites you can just do an XML export of pages/posts, import it on the new one, and then copy the wp-content folder over. There’s more in depth suggestions here:
https://codex.wordpress.org/Moving_WordPress
The reason I hold this opinion is that I think you want a smooth and clean experience, I think that’s why you used our one-click image. Newer versions of PHP and things like that, they won’t be part of Ubuntu 14’s base experience. You can add them, but any time you’re adding unsupported resources you run the risk of adding complexity that potentially breaks something. For your time, money, and sanity, I’d jump over to a new system. Bonus points, you get to benefit from all of the work that Ryan has been doing on our new one-clicks to improve them :)
Jarland