how to unlock passcode?

Welcome to the Apple Community.

If you can't remember the password you will need to restore the device.

I have this question as well, how to unlock my ipad mini.

If you can't remember your passcode, you'll have to restore it to remove the passcode, as explained here: http://support.apple.com/kb/HT1212.

If you're running iOS 7 with Find My iPhone enabled, in order to restore it you'll have to force it into recovery mode as explained here: http://support.apple.com/kb/ht1808, or erased it with Find My iPhone on icloud.com.