At the moment updating a VM kernel is touch and go. DigitalOcean's boot manager limitations mean that you can't install a kernel and reboot the machine into it. Instead you have to install a kernel (that exactly matches one available in the list) then select it from the dropdown in the admin interface. Many CentOS users update using yum update and bring all packages, including the kernel, up to the latest version.
That would be manageable (for 10s of 100s of VMs) if the list was frequently updated, but it's sporadic. The support team are very helpful and will update the hypervisor manually, if you:
1. shutdown the VM
2. post the kernel name in a support ticket
3. wait an indeterminable amount of time
4. restart the machine
That's not workable for dozens of VMs and/or production servers.
Please commit to regular, publicised updated times so that sysadmins can plan around them.