https://support.apple.com/guide/mac-help/change-the-login-password-on-mac-mchlp1550/10.14/mac/10.14

Change the login password on Mac

It’s important to change your login password from time to time to protect your privacy.

If you’ve forgotten your login password you’ll need to reset it. See Reset your Mac login password.

Note: Your login password is the password you enter to unlock your Mac when you turn it on or wake it from sleep. It is not your Apple ID password, which provides access to the iTunes Store, App Store, Apple Books, iCloud, and other Apple services.

1. On your Mac, choose Apple menu > System Preferences, then click Users & Groups.
   
2. Click Change Password.
   
3. Enter your current password in the Old Password field.
   
4. Enter your new password in the New Password field, then enter it again in the Verify field.
   
   For help choosing a secure password, click the Key button next to the New Password field.
   
5. Enter a hint to help you remember the password.
   
   The hint appears if you enter the wrong password three consecutive times, or if you click the question mark in the password field in the login window.
   
6. Click Change Password.