How to present a second ViewController & dismiss the first

You would need to first dismiss the "previousView" & then present the "nextQuestionViewController":

// Dismiss the first questionViewController
[previousView dismissViewControllerAnimated:NO completion:nil];

// Animates the next questionViewController using the first questionViewController
[previousView presentViewController:nextQuestionViewController animated:YES completion:nil];

I did next (self - is your old controller):

UIStoryboard *storyboard = self.storyboard;

[self dismissViewControllerAnimated:YES
                         completion:^{
        UIViewController *newController = [storyboard instantiateViewControllerWithIdentifier:@"newControllerStoryboardId"];
        newController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;

        [[UIApplication sharedApplication].keyWindow.rootViewController presentViewController:newController animated:YES completion:nil];
    }];

try

[self dismissViewControllerAnimated:NO completion:nil];

failing that:

[self.navigationController popViewControllerAnimated:YES];