How To Change The Name Of A NSStringFromClass From A Named Class in AppDelegate

How would I programmatically change the NSStringFromClass in Class c = NSClassFromString(@"ClassName"); in this if statement?

If Statement:

if ([vc class] == c2) {

        [self.window setRootViewController: vc];
         //THE CHANGED NSSTRINGFROMCLASS OF CLASS C HERE
    }