How can I make a UITextField move up when the keyboard is present - on starting to edit?

in (BOOL)textFieldShouldBeginEditing:(UITextField *)textField

if (textField.frame.origin.y > self.view.frame.size.height - 216)
{
if (screenHeight>500)
scrollView.contentSize = CGSizeMake(0.0, scrollView.contentSize.height + 100);
else
scrollView.contentSize = CGSizeMake(0.0, scrollView.contentSize.height + 216);
CGPoint scrollPoint = CGPointMake(0.0,(textField.frame.origin.y - (self.view.frame.size.height - 216 - textField.frame.size.height - 20)));
[scrollView setContentOffset:scrollPoint animated:YES];
}
[scrollView setScrollEnabled:YES];

when resigning keyBoard you need to write bellow code

scrollView.contentSize = CGSizeMake(0.0, 640);
CGPoint scrollPoint = CGPointMake(0.0,0.0);
[scrollView setContentOffset:scrollPoint animated:YES];