where are the physical memory cards located
In a PC, there's inside the case and mounted on the motherboard - the large circuit board you can see if you remove the side on your left as you face the front of a tower. In laptops, there's usually a small cover held down by a screw somewhere underneath the box. Be very careful handling them if you take them out - keep away from the gold bits.
I suggest turning the computer flat down on the opposite side (if desktop), and using a flashlight to look in. You can run Belarc Adviser first, and it will tell you what kind and how much you have.
Then go to crucial.com and take their little test to see if your memory is upgradeable. They will also suggest their own products. Write down the model # of the memory, then shop around for the best price with shipping. They're a perfectly reputable company, but you want to compare prices.