If you already know your current password and you just want to change it please see the following steps.

1. Click on the Apple menu icon in the upper left corner of your Mac.
2. Click on System Preferences from the drop down menu.
3. Click on Users & Groups.
4. Click the lock in the bottom left corner of the window to unlock the settings.
5. Enter your current Mac account password.
6. Click
7. Select your user account.
8. Make sure the Password tab is selected.
9. Click on Change Password.
10. Enter your current password under Old password.
11. Enter a new password. You can use your Mac’s Password Assistant to suggest one for you.
12. Enter the new password again under Verify.
13. Include a password hint to help you remember if you forget it in the future.
14. Click Change Password.
15. Click the lock again to save the changes.

If you don’t know your current password click here to see how to reset your mac’s password.