Replace the public key in ~/.ssh/authorized_keys on your existing instance so the attacker can no longer unlock it with their private key.

EC2 has changed quite a bit in the last five years, so whether you are new to EC2 or an old hand, it’s worth a look at how to launch your own EC2 instances today ...

Nick Hardiman shows you how to set up a secure connection to an Amazon EC2 machine using PuTTY and Pageant to handle your private key.