How to Modify Car Types For Stock in TRAINSET folder?, Newby missing something key Options

[Conductor Chris]

I am new with activity master and still figuring things out and one important thing has eluded me. How do I change the database of car types for the rolling stock I have? Changes made in activity master for car types of missing rolling stock and rolling stock used in the activity, that I understand - but changes made to existing rolling stock not used in the activity don't seem to "stick."

The current use is this:
I have the Monon II set from BLW, but not the Monon I set. I have freeware substitutes. I'd like to change locomotive types for the freeware I have to F3, C420, RS2 and so forth so I can change the types of the missing engines to match and get an appropriate direct replacement.

This must be simple, but I can't work it out or find it in the manual, so any help offered will be appreciated.

thank you
Christopher