Change key pair for ec2 instance

tip

Stop the running EC2 instance
Detach its /dev/sda1 volume (let's call it volume A)
Start new t1.micro EC2 instance, using my new key pair
Attach volume A to the new micro instance, as /dev/xvdf (or /dev/sdf)
SSH to the new micro instance and mount volume A to /mnt/tmp
Copy ~/.ssh/authorized_keys to /mnt/tmp/home/ubuntu/.ssh/authorized_keys
Logout
Terminate micro instance
Detach volume A from it
Attach volume A back to the main instance as /dev/sda1
Start the main instance
Login as before, using your new .pem file