What can I upgrade on a Samsung RV515?

laptops are restricted to 3 main upgrades:

RAM (the Crucial.com website seems to indicate that your laptop can accept an additional 4GB RAM bank (DDR3 SODIMM, 1066MHz of speed). This is useful if you have tons of windows and programs open, but with that processor I don't know if it's going to be so noticeably better.

Memory Storage devices (HDDs, SSDs, DVD drives can be removed and replaced with additional HDD/SSDs) These in general improve storage space (HDDs) or system responsiveness and load times (SSDs a lot, high end HDDs quite a bit but not anywhere near SSDs)

Battery (better endurance)

(theoretically you could upgrade processors as well, but it's extremely complex because they weren't designed to allow it to be done and anyway it's very very rarely worth it, given your lack of experience I'd discourage that course of action)

This is the price for having something portable. If you don't need something portable, investing in a good desktop computer would give tons of bang for your buck.

I'd personally save the cash for a new one, either laptop or desktop, if you really want to see improvements.
Say what you'd like to do with it and someone will point you in the right direction.

You can post a new thread to ask tips on what to get for the new computer, possibly in the gaming section.
Being inexperienced you could blow money in well-marketed but inferior products.