There are two main methods.
From within the IDMS system, type the command DCPROFIL.
The top line of the output will show something like this:
The six-character value identifies which release this system was installed from.
The middle two characters, in this case J0, indicate the version.
J0 = r19.0, I5 = r18.5.
Also in the startup joblog, this message can be used to identify the release:
IDMS DC390009 V65 STARTING IDMS-CV/DC INITIALIZATION - R19.0 SP 4