In Amazon Web Services (or AWS) EC2; compute instances can be upgraded/downgraded when stopped. However, I'd like to know which instance types are available even when the instance is running, even if I have to stop it to do the upgrade/downgrade. So, is there an API or console interface that will tell me what instance types are available upgrade/downgrade for an instance while its running?
No. You cannot upgrade ANY instance while it is running. When upgrade your instance, it is most likely run in a different hardware. So without stopping the instance it is impossible to move our instance to a different physical machine. There is no such thing like vMotion in AWS.
I see update to the question. There is no matrix for instance upgrade. There are many factors that affect this:
Take a look at: Resizing Your Instance