How to remove passwords, pass codes
I will be giving away my iphone 6plus
but its locked.
Question marked as
What to do before selling or giving away your iPhone, iPad, or iPod touch - https://support.apple.com/HT201351 - "Use these steps to remove your personal information from a device, even if you don't have it anymore."
The above may work to remove the passcodes too but if it doesn't then:
If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - http://support.apple.com/HT204306