Like Gordon nicely noted, there have been many,many changes between the release
of CUCM 6.x and the newly released CUCM 8.6. I have tried to keep a running doc
that highlights the changes between 4.x and 8.6 but it is by no means comprehensive.
It might help for your task though
Don't forget as well that CUCM 6.1 has been announced as EoL (end of life)