You are confusing RAM which is where programs run with hard drive space which is where data and programs are stored. The 2009 MBP cannot be upgraded beyond 8GB. For most people that is sufficient at the moment. If 8GB isn’t sufficient for your needs swapping out the original hard drive for an SSD is a very worthwhile upgrade. In fact, in my testing 2 years ago I found that for my use the SSD upgrade was more effective than the RAM upgrade.
One reason people sometimes confuse RAM and storage is because of something called virtual memory. Modern computers are built so that if we try to load too many programs for the amount of memory we have, instead of saying “No, can’t do that” the computer copies a block of RAM that isn’t being used at the moment to the hard drive. It then uses that bit of RAM for the program we want to run. Later if that block needs to be placed back into memory the computer swaps out the RAM for what’s on the hard drive. With a mechanical hard drive during those swaps we’d generally see the beachball or we’d notice the computer slow down for a couple seconds. The SSD is so fast that we notice nothing happening at all which is why an SSD upgrade can be more useful than a RAM upgrade if your computer still has a standard hard drive.
