If you don't know the Apple ID and Password the only way to remove Activation Lock is to contact Apple. You will need to provide the receipt that shows the SN and your name before they will remove the Activation Lock.
If you don't have that, your best bet is to try and remember the Apple ID. At that point you could go to the Apple support site and try to reset the password. Once you have both of those you can turn off Activation Lock on the device or from iCloud.com.