I have a GT 610 running on a ~305 watt PSU and it's just fine (or at least from what I see). 225 watts is pretty damn low for a PSU, seems like the computer wasn't really made to be upgraded much(or really at all). I'd highly recommend one at least 400+ if you plan to stick with what you have. If you plan to just buy a whole new PC, use
pcpartpicker.com. If you can afford it, I'd recommend a GTX 760 (which would definitely need more than the 225 watts of power you have, which means your going to have to build a PC from the ground up), but if you can, aim for a GTX 770+ which should be more than enough for the games you want to play (other specs like RAM, CPU, PSU, etc. allowing).
EDIT: A Geforce 650 Ti should also be more than sufficient for the games.