But if you don't want to make the image any smaller dimension-wise, choose "Save As" under the Edit menu and you'll see the adjustment for Quality (I think that's what it's called in Photoshop, I'm using Gimp these days--or Compression possibly).
You should be able to get an 800 x 600 pixel image down to 50 kilobytes or even less this way.
You likely won't see that option if you just do a "Save". With "Save As", you have the options to either write over the original, rename it, or save in a different location.