You can update the UIStepper size and therefore set any size increment and decrement images.
Use the following method to set the background image and the stepper will draw itself using the background size:
- (void)setBackgroundImage:(UIImage*)image forState:(UIControlState)state
Example
[self.stepper1 setIncrementImage:[UIImage imageNamed:@"plusIcon1.png"] forState:UIControlStateNormal];
[self.stepper1 setDecrementImage:[UIImage imageNamed:@"minusIcon1.png"] forState:UIControlStateNormal];
[self.stepper1 setBackgroundImage:[UIImage imageNamed:@"stepperBkg1.png"] forState:UIControlStateNormal];
[self.stepper1 setBackgroundImage:[UIImage imageNamed:@"stepperBkgHighlighted1.png"] forState:UIControlStateHighlighted];
[self.stepper1 setBackgroundImage:[UIImage imageNamed:@"stepperBkgDisabled1.png"] forState:UIControlStateDisabled];
This yields the following result on the left, compared to an unmodified stepper on the right:
stepperBkg1@2x.png:
stepperBkgHighlighted1@2x.png: