This appears to be, from what you've provided, a small form factor HP desktop with an Iris-A6 motherboard. Does your motherboard look like this?
If so, your upgrade options for anything other than RAM and hard drive are very limited. This motherboard comes with an AMD A6-7310 and is not upgradeable. There is also no PCIE slot, so there's no option to add a GPU.
Unfortunately, basic, entry-level PCs with small form factors are frequently not candidates for upgrading. Unless the amount of RAM is the limitation in a specific game -- and you'll be limited by the APU before you run into RAM problems in gaming -- the games that it runs will always be the games that it runs and if...