Eric Hammond suggests how to transition to a new version of Ubuntu using an Amazon EC2 instance. Wow!
Posting it here for future reference.

> Simon:
> Assuming you're not running EBS boot instances, you cannot upgrade the
> kernel in place. Even if you are running EBS boot instances, upgrading
> in place can be a bit messy and probably should not be tested first on
> your live systems.
> If possible, I recommend you start with the latest 9.10 AMIs and build
> your systems on new instances.
> If you have built extensively customized private AMIs, and you did not
> automate or document the software installation and customization, and
> you really want to try upgrading without starting from scratch, here is
> an approach which could let you test this without risking your currently
> running instances, but it gets complicated:
> - download the custom AMI bundle from S3
> - unbundle the image
> - create an EBS volume
> - copy image file system to the EBS volume
> - snapshot the EBS volume
> - register the snapshot as a new EBS boot AMI with the old aki+ari
> - run a new instance of the EBS boot AMI
> - upgrade the system in place
> - snapshot that instance's EBS volume
> - register that EBS snapshot as a new new AMI with the newer aki+ari
> - run a new instanced of the new new AMI and test
> - clean up the temporary instances, EBS volumes, and EBS snapshot
> You could also save the image as an S3 based AMI if that's what you want
> to run.
> I'm not sure if solicitation is allowed on this list, but if needed, I
> could help with this kind of small task.
> My standard recommendation, however, is to always start with fresh
> public AMIs and document/automate the installation of your
> customizations so that you can switch to new public AMIs whenever they
> come out. Whether you run the installation scripts at boot time or run
> them to create private AMIs depends on how long they take and how
> quickly you need new instances to start.
> --
> Eric Hammond