Decrease the margin of content of UIPickerView ios

Modification due to the first 2 answers : what I want to modify is not the height of the UIPickerview. What I want is to make the content of UIPicker begins from the upper side of UIPicker. Here is an example:

I want to delete the margin shown in the image here attached.

Any idea?

With a toolbar, the UIPickerView is embedded in a UIView. So the view hierarchy is : View(parent)->Toolbar(child), UIPickerView(child)

The View is declared as customPicker in my viewController. Here is the code: In viewController.h :

@interface myViewController:UIViewController<UIPickerViewDataSource, UIPickerViewDelegate>

@property (weak, nonatomic) IBoutlet UIView *customPicker;

@end

In viewController.m :

- (void) viewDidLoad{
self.customPicker.frame = CGRectMake(0, CGRectGetMaxY(self.view.frame), CGRectGetWidth(self.customPicker.frame), CGRectGetHeight(self.customPicker.frame));
    [self.view addSubview:self.customPicker];
}

Then I use a setPickerHidden method to animate the View in order to show or hide it.

Thanks in advance for your help!

That is not possible. If you need differently styled "UIPickerView" you will to roll your own.