How to remove the icloud acct and sign in my newa

Welcome to the Apple community.

Unfortunately, you cannot do very much with your phone unless you get assistance from the previous owner, they should either provide you with the password to unlock it or remove their account from the phone entirely remotely through iCloud.com > Find My Phone.

and what can i do if the previous owner does not remember his icloud username and password?

camillegerv24 wrote:

and what can i do if the previous owner does not remember his icloud username and password?

nothing.

ask for your money back.