Have you seen this link? It has the steps you need
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/virtual/servers.html
See here for direct upgrade paths, as long as you are at 6.1(4) or higher, you can jump directly to 8.5 or 8.6
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/compat/ccmcompmatr.html#wp43011
Thanks
Srini