In the event that you forget your root password, you can very easily reset it through the HostDoc client area.
First, log into your HostDoc account.
Then, scroll down to the menu and select the icon.
Put in your new password, and then confirm it in the next box. When done, click the button.
Once you have done that, you will need to restart your VPS. You may now log into your VPS with the new root password.