There are several steps to reset the root password on an Ubuntu server. Here are some general steps to follow:
1. First, power on or reboot the Ubuntu server.
2. On the boot loader, select the "Advanced options" for Ubuntu and select the Recovery mode.
3. Once in Recovery mode, select the "Drop to root shell prompt" option.
4. Remount the root filesystem as read/write by entering the following command:
mount -rw -o remount /
5. Run the command "passwd root" to change the password for the root user.
6. Enter the new password twice, as prompted.
7. Once the passwords is updated successfully, type "exit" and select the "resume normal boot" option to restart the Ubuntu server normally.
Note: Keep in mind that resetting the root password may have security implications and should only be done if absolutely necessary.