If you are the owner of the computer, one thing you must have and you must keep, is an administrator password. Don't forget the password, write and keep it in the safe place.
Because we are human, forget can be experienced by anyone.
If you forget Apple Macbook administrator password, below you will get the trick with easy.
Shutdown the Macbook
Switch on again Macbook, press and hold the Command+S (on the keyboard, see figure) during start
Holding the Command+S wait until prompt appear (after the root# appear, see figure), if already, release the keys (Command+S)
sbin/mount -uw / then hit Enter
rm -rf /var/db/.AppleSetupDone then hit Enter
Reboot then hit Enter
The 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).