If you open up the back of the organ, there should be a bag of screws and a chart. You can study the chart-but I wouldn't mess with it unless you really know what you're doing.
I can't think of a reason why you would want to change those anyway because if you have a B3 or C3 style organ, you've got four different ways to set up the manuals for any drawbar position that you want.
I would suggest at the least, if you HAVE to mess with the factory set up, draw a chart for what it looks like before you mess with it so that you can return it to the way it was.