See if you can remember them. If not, the device will just think you are a thief trying to hack your way in.
"Activation Lock for iPhone, iPad, and iPod touch" is a security feature, in part to deter re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365
An activation lock can only be removed using the log-in information for the account that applied the lock. If you know this information click on the link to read how to "Turn off Activation Lock." --> https://support.apple.com/HT201441
Since you are the original owner and have forgotten the log-in information, try to recover it:
"If you forgot your Apple ID" [this is likely an email address you are using or used in the past] click here --> https://support.apple.com/HT201354
"If you forgot your Apple ID password" click here --> https://support.apple.com/HT201487
Otherwise:
Apple may possibly remove a lock if a person can provide sufficient evidence of valid ownership. The device is normally taken to an Apple Store with identification and the original sales receipt. I.e., the receipt when the item was sold to the first owner, and preferably by that person. This is unofficial and there is apparently no set policy (I asked at an Apple Store). A store may simply refuse, particularly if they are not satisfied you have proven ownership by provenance.
Now is also the time to remember that in this digital age, things like passwords have real $ value. It is worth keeping a book somewhere with all your accounts and passwords written down. I am fortunate that my email address hasn't changed in 30 years.