Normally insulating a concrete floor is done ONE of two ways.
IF the floor is already poured you can DIG away on the outside. Dig down At least 2 feet and install 2" EXTRUDED polystyrene. DO NOT use the EXPANDED (white bead board like a foam coffee cup) polystyrene. IF you have Incredible patience and ability you can/should install it down 4' but if you can get at least 2' that will do 80% of the job.
IF you have not yet poured the concrete, You can do it Several ways. Install the 2" Similar to the images below: