1. Boot the system and when you see the following message "Press any key to enter the menu", press any key. (You will see the list of available kernel versions.)
2. Press e in order to edit commands before booting.
3. Highlight the list item with vmlinuz in it by using the arrow keys and press e.
4. Now type single or init 1 at the end of the line.
5. Then press enter and b to boot the system with the new argument. (The system will boot into single user mode and you will see bash prompt)
Now it’s time to change the password:
### Shell Commands ###
Enter new UNIX password:
Retype new UNIX password:
: password updated successfully
7. Type reboot to restart the system.