Turn off Find My iPhone Activation Lock (formerly: Activation Lock: Removing a device from a previous owner’s account) - https://support.apple.com/HT201441 - If an activation lock was put on a device, only the owner of the account that applied the lock can remove it.
If you forgot your Apple ID - https://support.apple.com/HT201354
If you forgot your Apple ID password - Apple Support - https://support.apple.com/HT201487