1. If needed, force .NET garbage collection using the following code:
Note that this will temporarily block the session. Therefore, to minimize impact it's recommended this is done in the clean-up steps of a program and only if the program causes excessive memory usage.
2. Alternatively, explicitly DELETE OBJECT the instances that are no longer needed. This will free up the resources on the ABL side, and will help ensure that the .NET portion becomes garbage-collectable.