yes for a matter enfact i do know where to upgrade your cars at there is one in san feirro SAN ANDREAS
basicaly it is accross the street from the house you get from when you just unlock the city but not really it is like from when you save it you
are facing away from the house you know so when your facing that way turn left and go down the road to the car dealer ship that just have glass windows and go behind it is a PAY IN SPRAY where you can give your car a diffrent paint job but you cant choose it but when your on the otherside of the dealer ship go to where you are facing where it shuts to give yourself a paint job and turn around then there will be a road follow the road till you see a TRANSFENDER the door is closed but
you can CHOOSE YOUR PAINTJOB, GET NOS, GET A SPOILER, GET A SIDESKIRT, GET DIFFRENT WHEELS, AND BEING ABLE TO GO!!!!!!!!!!!!! PIMPING!!!!!!!!!!!!!. THIS CAN BE USED FOR PS2, XBOX360, OR PS3