You use Illustrators basic Drawing Tools to trace the Images. Like that you get a redrawn vector-version of your image. There's lots of Information about the usage of basic Illustrator drawingtools here on StackExchange.
You use the Autotrace function of illustrator. In the Object menu you find Image Trace. Use it while you have your picture selected. There's Options on how your Image is retraced in the Optionbar ontop of your screen. Tutorial: Image Trace in Adobe Illustrator CS6.