You can put a GPU in that system, as long as it will fit. It is hard to see form the pictures of the case, but I would open it up and measure the distance from the back of the case where a GPU would go and see how much room you have.
You can get small 1050ti's and 560's that should fit. It does not say how big the PSU is, but it is probably 300 watts and it probably not very good. But the 1050ti and 560 don't require a lot of power, so it should work.