Paint Shop Pro is an even more popular and affordable all-purpose image editing powerhouse one used by many pros as well. I know little about Paint Shop Pro , but it does layers and tone curves and enjoys a very enthusiastic RPD following. I won't get into the pros and cons of various photo editors here, but the software links on this site's home page are a good place to start your own research. Since I can't improve on Paul's words, I've quoted them nearly verbatim with his permission, of course. Hopefully they'll inspire you to get to work on your photos with whatever tools you have.
Curves tool a try.
When I first tried Curves I hated it, probably because I was overdoing it. The key is to make tiny adjustments. The beauty of this tool is that it increases contrast without over or under-exposure. Make tiny adjustments and see the huge differences they make. The key is not to overdo it.