A picture might help. There are various methods of holding light fixtures in place with springs. If you can get a little inspection mirror, say a cheap dental mirror, that can be really useful for observing how it's put together within the recess. (The dollar stores, at least the ones around me, sometimes have kits that include a dental mirror along with a toothbrush and various other dental implements.)
If the springs form a parallel pair of vertical spring wires on either side as the light unit is pulled down, frequently you need to squeeze them towards each other to unhook the upper ends from their retainers.