With some assistance from Jackie, I ordered a new memory stick for my laptop, and I managed to put it in. I misunderstood the procedure, so the first time I took the cover off I couldn't get the memory in, but at least I didn't break anything, and after Jackie pointed me to a website explaining the procedure, I tried again and got it.
With 8 GB instead of 4, surfing the web is now much less annoying. (I like to leave any web page that I'm at all likely to look at again open, so I frequently have 50+ tabs open. This seems to me perfectly natural, the whole reason browsers have multiple tabs, but the performance is so bad that it's apparent that the average computer user either doesn't do this, or has a lot more RAM than I expect for a low end machine.)