Can we upgrade without release key
i have a vcs appliance running with 8.1 version
Yes you can upgrade Within a Major Release
X8.x.x to another X8.x.x version without a release key.
You require a release key when going from X6 to X7 or X7 to X8 etc.
I have one more question
i am using TMS 13.2.1 or MCU 4.3
these are support with vcs 8.5 or i need to upgrade my both appliances.
This question is dependent on the applications you are running off TMS if there are any interop issues there
The release notes state Interop issues for using below TMS 13.x.x but this is something you will need to look at in your organisation at what else is running in the environment that upgrading the call control might interfere with.
For example x8.5 has a load of remote mobile clients which require different firmware etc.