If you don't have access to photo editing software like Photoshop or Elements, there are several free or lowcost alternatives. One I like to use because it's quick and it's linked to Flickr is called Picnik. You can upload your photos and edit them on their website for free. For an annual fee, you get access to more editing tools.
The photo above is one of the photos I took on our trip to Alaska last month. I used Picnik to sharpen the photo and tweaked the saturation a little...I like the result.
Here's the original photo for comparison: