Darren has the easiest answer. Lots of gain for little cost.
There is another way to maximize what you have, too. When you load a photo into your computer, there is a great deal of embedded formatting in each image file. I discovered by accident long ago (c.2003) that if you open your image in an image program - even Paint - and then save it, many kilobytes of such formatting is stripped away, making your image file a smaller file in terms of Kbs, while not loosing clarity or definition.
Also, resizing images helps a lot. Until recently all the images I posted were a maximum of 600-800 pixels and that range looks real good. I can't speak for today's screens because my PC is from 2010.
It's a pain to open each image and resize/re-save. But it is effective.