I am giving my old Macbook away. How do delete all memory and myself as the Admin user ?

Please follow the instructions in this Apple Help page:

What to do before selling or giving away your Mac - Apple Support

Click here and follow the instructions. If the computer originally shipped with Mac OS X 10.6.8 or earlier, when you reach step 5, insert its original disk, restart with the C or Option key held down, use the Disk Utility to erase the internal drive, and install a fresh OS.

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