How do I remove a old account ?

If it is signed into someone else’s AppleID in iCloud, you cannot remove that without knowing the password used with that AppleID. Ask the seller to remove it (they can do so by following these instructions - Turn off Find My iPhone Activation Lock - Apple Support), or try to get your money back.

Not sure what you are asking. See if this helps: https://support.apple.com/en-us/HT201351

How to delete your Apple ID account - Apple Support, but there is no reason to delete your Apple ID. Perhaps you could be more specific?