I have windows 7 and I really can not find how change picture format without photoshop! Have windows 7 any standard program to do it?
Most image editors or image viewers let you save the picture you have opened in them in a different format. This is the easiest way to "convert" to a different format most of the time.
Examples include Irfanview (lightweight), GIMP, Ulead's iPhoto Plus!, and MS Paint. Irfanview (with plugins) is my personal favorite for this task. There's many others.
You can install Imagemagick to use the