You are confusing your memory (RAM) use with storage (hard-drive) you really need to add another 2GB of RAM in your PC. Did you buy it with only 2GB installed or have you upgraded an older PC to windows 7. Either way if you use this. Crucial Scanner this will tell you what RAM you can install. Now you do not have to buy from Crucial but do take a note of what RAM you have then buy 2GB elsewhere as Crucial is not the cheapest.
How to get Windows 10 now: how to download and install Windows 10 even if GWX.exe is missing