iPhone 5 iOS 8.0 - Forgot my apple ID password & cannot restore the password

I received my dad's old iPhone 5. He remembers the password, but he cannot remember his Apple ID's password, nor the security question, nor the password for the email linked to this account. I can access the phone, even jailbreak it, but how can I remove or change the password of the Apple ID?

There's no way to reset the password of the Apple ID if you don't know neither the answer to the security question nor the password to the email account linked to the Apple ID.

However, you can easily remove the Apple ID from your iPhone. To do this:

1. Go to Settings > iCloud.
2. At the bottom of the page, tap Delete Account.
3. Tap Delete to confirm.