tips and advice for toning!!!!

I want to loose my lower stomach ... (underneath my belly button).... I need advice and tips of how to do so without putting too much stress on my joints since I have what is called Runners Knee or floating patella... my knee moves out of place so I can't do a lot of running. 
What exercises would you recommend for Lower belly workout to get rid of a that area (lower stomach under belly button)  
If you can attach pictures or links that would be great and so much appreciated!!