Andrew R Stewart 

These guards are often help on by both screws (and I see two, likely a third present) and plastic finger or tab in slot designs. Usually the axle nuts and washers need to be removed in addition to any screws. Then one does the wiggle, pry, prod dance to remove the guard without damaging it's plastic interfacing parts. Sometimes the guard is in two parts, one main part surrounding the chainring and extending back to about the rear axle and another pars that slips on from the back and covers the rear cog. Sometimes the rear wheel needs to be able to be slid fore or aft in the drop out (and thus the coaster brake reaction arm bolt would also be removed). Sometimes the RH pedal (the one with common right hand threading, like a light bulb's) needs removal, as it seems by the image. Sometimes the guard's mounting clips should be removed from the frame. So it all depends on the design and the image doesn't show enough views and details for us to say much more. Andy