I must offer my suggestion to this with a tutorial.
First of all, yes you can change the password, in fact it is quite simple.
1. Login to your droplet as root
2. type the command "passwd" (no quotes) and press enter
3. Type in your new password - PLEASE I BEG YOU... use something with upper and lower case and a number or two and a symbol
4. Confirm the password
5. YOU ARE DONE!
When it comes to using SSH Keys, I have issues with this, unless you know what you are doing, please don't While it is more secure than a password, there are issues with it. If you need to have a developer help you with some things it is easier to give him access using a username/password with privileges that YOU choose. Also, if you are using the droplet for a day or 2, having SSH Keys is nice, but not a major thing.
I hope that helps answer your question