Change key pair for AWS EC2 instance

1. Stop the running EC2 instance.
2. Detach its /dev/sda1 volume (let’s call it volume A)
3. Start new t1.micro EC2 instance, using my new key pair
4. Attach volume A to the new micro instance, as /dev/xvdf (or /dev/sdf)
5. SSH to the new micro instance and mount volume A to /mnt/tmp
6. Copy ~/.ssh/authorized_keys to /mnt/tmp/home/ubuntu/.ssh/authorized_keys
7. Logout
8. Terminate micro instance
9. Detach volume A from it
10. Attach volume A back to the main instance as /dev/sda1
11. Start the main instance
12. Login as before, using your new .pem file