how can I delete a user from my Mac book

The " Owner Account of this computer "  has that privilege to add, remove, upgrade or downgrade accounts.

This would include adding more Admin Accounts and / or downgrading an ADDED Admin account plus Remove an Account  

Set up users, guests, and groups on Mac

Normally the " Owner Account  " is the very first Account used when the Computer was Very First Setup as New and out of the box.

Adding or Removing additional Admin Account can be done there after.

You can do this as an administrator in System Settings/User & Groups.

Have a look at this article:

Delete a user or group on Mac - Apple Support