In this screencast I will show you how you can replace a running EC2 instance with a larger one. You may want to do this if you find that you need bigger and better hardware to serve your website, or to move from a development system to a more powerful production system.
In this example my EC2 instance is an M1 Small which hosts a single WordPress website with about 500-600 hits per day. In the screencast I'm replacing it with an M3 Medium instance which really isn't big enough to cope with the traffic. I have since found that a C3 Large is a better fit. The total downtime to perform this depends on how big your current instance is. You can bring up a larger instance alongside a smaller one and then swap the Elastic IP over for minimum downtime.
If you have any questions, please leave a comment.