Upgrade 1.810.210.57-1 to 5*?

I’m currently running 1.810.210.57-1, is there a clean method to upgrade to 5.211.65-8?

No as CentOS has no upgrade path from 5.X to 6.X. You need to reinstall. Please see http://wiki.freepbx.org/display/FD/FreePBX-Distro-1.8xx.210.58

Thanks Tony! Much appreciated.