The most glaring problem actually isn't even if it has a slot it's actually that the power supply isn't big enough under load a GTX 550 uses 248 watts of power and the computer comes with a 300 watt power supply. Even idle the card uses 139 watts, so before you can even think about putting that card in you would need to upgrade the power supply.
It does have a x16 slot available in the motherboard for plugging in a seperate video card however.
^^ oops beat me to it
sorry i was replying to the other guy,but what power supply do you recommend and how much will it cost?