How to change the Font size in UIPickerView?

Update in Swift for iOS8, you can add this to your delegate:

func pickerView(pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusingView view: UIView!) -> UIView {

    var pickerLabel = view as? UILabel;

    if (pickerLabel == nil)
    {
        pickerLabel = UILabel()

        pickerLabel?.font = UIFont(name: "Montserrat", size: 16)
        pickerLabel?.textAlignment = NSTextAlignment.Center
    }

    pickerLabel?.text = fetchLabelForRowNumber(row)

    return pickerLabel!;
}

You need to implement pickerView:viewForRow:forComponent:reusingView: method in picker's delegate

- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view{
    UILabel* tView = (UILabel*)view;
    if (!tView){
        tView = [[UILabel alloc] init];
            // Setup label properties - frame, font, colors etc
            ...
    }
    // Fill the label text here
    ...
    return tView;
}