1/ You can try resetting your password:
When you are asked for your Apple ID and password, there is always a link "Forgot your password?" Click on it and follow the steps. You'll be asked security questions or get sent a link by Email to reset your password. If you can't remember your security questions/answers or don't have access to your Email, try step 2.
2/ Find an Apple Store or Apple Authorized Service Provider and provide them with proof of purchase of your device and they will unlock it for free.
Or contact them through their website: https://support.apple.com/apple-id for the same.
3/ By hardware or going through websites that remove the Apple ID from your device: expensive, time consuming, often worth more than the device; in some cases not definitive and may get locked again. I highly recommend against this 3rd option.
We sell and repair Apple products for a living. When someone at the store approaches me for this reason, I always only try steps 1 and 2.