How do I convert Linode CentOS 5.x VPS to CloudLinux

Start with this guide to prepare for custom CentOS kernel:
http://library.linode.com/linode-platform/custom-instances/pv-grub-howto#sph_centos-5
After that use standard way to convert from CentOS to CloudLinux:
http://www.cloudlinux.com/downloads/
Once you are done, in the Linode Manager, edit your Linode's configuration profile to use pv-grub-x86_64 (or 32bit one if you use 32bit arch) as the "Kernel". Make sure the root device is specified as xvda. Save your changes by clicking "Save Profile" at the bottom of the page, and reboot your Linode from the "Dashboard" tab.