For begginners.
If you are a begginer, the easiest thing to use us Splashup ( light ). There is also a more advanced Splashup, but for your needs the light version is good enough. Just search for it on the internet and download it for free. It will probably be all you need for now, let us know how you like it.
My experience with GIMP is that it is too complicated if you just need simple. Infranview is complicated and useless. Photoscape and Picassa is OK, but to get the same simplified go with Splashup ( light ).