Updating an AMI’s Kernel and Ramdisk
http://developer.amazonwebservices.com/connect/entry.jspa?externalID=2865
In order to upgrade your AMI to the latest kernel you will have to launch your existing AMI and rebundle it explicitly overriding the default bundling tools behavior – which is to use the instance meta-data service to determine your current kernel and ramdisk combination OR overriding the launch time kernel and ramdisk parameters.