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If you can't change your password using your Apple ID, you can use Recovery Mode to reset it. Recovery Mode needs to be accessed as your computer is starting up. ⌘ Command+R as soon as you hear the chime. Continue holding the keys until you see the loading bar appear. This will boot your Mac into Recovery Mode. It may take a while to load. You'll see the Utilities menu in the bar at the top of the screen. resetpassword and press ⏎ Return. This will open the Reset Password utility. If you have multiple drives in your Mac, you'll need to select the one that your operating system is on. This will typically be labeled "Macintosh HD." Use the drop-down menu to select your user account. Enter your new admin password twice to create it. This hint can be displayed if you're having difficulty logging in. It will be applied when you reboot your computer. Opt to restart your Mac when prompted. This will reboot your computer and apply your new password. After rebooting, select your user account and log in with your new password.

Summary:
Reboot your computer. Hold . Click the "Utilities" menu and select "Terminal." Type . Select your hard drive. Select the user account you want to change the password for. Create a new admin password. Enter an optional password hint. Click "Save" to save your new password. Click the Apple menu and select "OS X Utilities" → "Quit OS X Utilities." Log in with your new password.