Revoke access with specific private key to an EC2 server

Question

I have converted my PEM file to a PPK file and I can successfully connect to the EC2 through Putty or FileZilla using the private key.

Lets say we have a scenario:
I request a new PEM and give the new PPK to somebody. Now I need to stop or refuse access to the server using that particular PPK.

How would I proceed?

(As I understood by reading the documentation, each EC2 instance gets a unique (default) key pair when you create it. The only way to change the default key pair would be by terminating the instance.)

Answer 1

Check all allowed public keys by

cat ~/.ssh/authorized_keys

Find and remove your particular public keys to revoke access.