I have running Ubuntu 10.04 instance with EBS storage. Current type of my instance m1.small. I want to increase cpu performance, so I guess I should "convert" that instance to c1.medium. How can I do that? Can I do it "on fly" or I should stop it first?
Think of it as moving your harddisk to a new computer. You need to boot a c1.medium instance with your AMI.
Depending on how your software is set up you can keep the current instance running in the meantime and 'failover' to the new instance. Otherwise shut the old one down and boot the new instance. In any case, it cannot be done 'on the fly'.
You can stop the instance and restart it with a different type http://aws.typepad.com/aws/2011/03/even-more-ec2-goodies-in-the-aws-management-console.html
The types m1.small and c1.medium are different machine types, with different memory and CPU capacities. You can't seamlessly move between physical hardware -- you'll have to create a new and larger instance, and then fail over to the larger machine.
Simon @ http://LabSlice.com - Virtual Lab Management on EC2