About the Media Gallery Module
You should use Firebug and take a look at the function that gets called, when clicking on the "Next"-Button.(Something like onClick() )

Now take a look at the function, that gets called, when you click on the image.

Now just place the "Next"-Button function into the image. Delete the old one.

The functions are usually in a .js-File. 

This is not so hard, i am a beginner and managed it with the shadowbox.