If you are the owner of the computer, one thing you must have and keep is an administrator password.
In this post, i will tell you the way to reset Macbook administrator password if you forget it.
This trick is to create the new administrator account, so after creating this new administrator, you can manage other accounts.
Shutdown the Macbook
Turn on the macbook again, immediately put your pingers on the key: Command and S, press and hold these keys (command+S).
Wait for a moment until the :/ root# appears, see the figure.
Then Write:
sbin/mount -uw Enter
rm -rf /var/db/.AppleSetupDone Enter
Reboot Enter
Macbook then will restart,
Next you will get the wizard to to fill the information, new user/administrator name and new password, and other information.
you need to have an internet connection (wifi is recommended).