Depends on what GTX 750 you get, some require a 6 pin PSU connector if they do then you cant, but some take power from the motherboard and nothing else if they do that then you can, but for future upgrades I would always recommended getting an upgrade unless you already have a 650W 80+ Gold, if you don't think you will be doing a big upgrade apart from what you are asking about now then stick with what you got and get a 750 that dosent need a 6 pin power supply and you should be fine