Extend the drawer you want to remove from your stack-on tool chest fully into the "open" position. Pull it out as far as it will go.
Examine the sides of the drawer. You will see one metal or plastic track on each side of the drawer. Toward the back of the drawer will be the mechanism, typically a lever of some kind, that is holding the drawer in place.
Adjust the lever on the left side of the unit so that it releases the drawer from the track. Either push down on the lever, pull up on the lever or pull out on the lever, whichever is applicable, to release the drawer.
Adjust the lever on the right side of the unit so that it releases the drawer from the track. Push the lever whichever way you did for the left one to release the drawer.
Use your hands to physically separate and remove the drawer from the stack-on tool chest.