An EC2 instance needs to be stopped before it can be resized. Also, it can only be resized to a "compatible" type (ie, one with a compatible kernel, 32 bit or 64 bit). So, if you started with a 32 bit t1.micro you can only resize up to a 32 bit m1.small. If you started with a 64 bit t1.micro you could resize up to a 64 bit m1.large.
wintermute:~ $ ec2-stop-instances i-3e15ff51
INSTANCE i-3e15ff51 running stopping
wintermute:~ $ ec2-modify-instance-attribute -t m2.2xlarge i-3e15ff51
Client.IncorrectInstanceState: The instance 'i-3e15ff51' is not in the 'stopped' state.
wintermute:~ $ ec2-modify-instance-attribute -t m2.2xlarge i-3e15ff51
instanceType i-3e15ff51 m2.2xlarge
wintermute:~ $ ec2-start-instances i-3e15ff51
INSTANCE i-3e15ff51 stopped pending
By the way, these short posts are essentially notes to myself while working (I keep forgetting the syntax!). I've got some Cherokee-related posts in the pipeline, I just need to find some extra spare time at night.
In the meantime, follow me on Twitter, it's free.
