Might have accidentally change admin user to standard user
To create a new admin user, you need to reboot into Single User mode once:


Boot to single user mode (⌘-S while powering on)
Run /sbin/fsck -fy
Run /sbin/mount -uw /
Run rm /var/db/.AppleSetupDone
Run reboot


After the reboot, the Setup Assistant should get displayed again (as for a new Mac) and prompt you to create a new user. This user will automatically have admin rights.