How to free the graphics from memory

I'm currently working with torque 2d, and I would like to know how it handles memory. I know how to load images using the t2dImageMapDatablock, by creating an instance of the the datablock (datablock FlyingVehicleData(F117NighthawkBlock){}), but I don't know how to free the memory. I would like to be abble to load all the necessary images before a level is started, and then free up memory once it's finished.

Do someone know how to do that ?

thanks