You can reset the root password for your droplet from the control panel. A new temporary password will be emailed to you. You’ll then need to log in via ssh or the console and set a new permanent password to replace the temporary one.

Once you’ve regained shell access you should investigate. Your root password will not change on it’s own and unfortunately WordPress sites are a prime target for attackers. You’ll need to make sure your droplet is not compromised.

There are several methods available then to reset your WordPress user’s password.