At this point, your new public key should be on your EC2 instance in the authorized_keys file, and all you have to do is remove the old one.

Brien Posey shows how to access EC2 virtual machine instances through the use of key pairs via the AWS CLI or PowerShell.

AWS allocates IPs for your EC2 instances using internal DHCP, it will change whenever you shut it down. If you associated an Elastic IP with the instance, that association will also have been lost.