Yes there are various free programs to edit your pictures. The leading free photo editing program is Gimp which is very similar to Adobe Photoshop and has almost all the abilities of Photoshop. Gimp is free ware not share ware or a demo version you must buy later or to get full use. You can edit, adjust exposure, crop, change colors and do all kinds of things to your photos using Gimp. Gimp works with almost all types of photo files and works easily with JPG which is the most common. Gimp is available at www.gimp.org It has menus that are similar to Photoshop and has come a long way. Gimp will work in Windows, on Linux and on the Apple Mac computers.
Other free photo editing programs are built in many of the photo storage/printing services. You can edit your pictures using software at Shutterfly (www.shutterfly.com), Flickr (www.flickr.com), Picasa (picasa.google.com) and others. However with these photo sharing services the abilities to edit your pictures are more limited. Many scanners include a photo editing program with the scanner.
There also apps available to edit your photos on your smart phones.
Adobe Photoshop is the recognized leader in non-free photo editing software and has a limited version called Photoshop Element that is much cheaper and a professional version called Photoshop CS or CC and can be bought or subscribed to on the cloud. The current version is CS6