iPhone 4s. When sending texts I turn the phone sideways and the screen turns around to suit so I have a bigger typeface. Some way or another it has locked in one position and won't turn around any way at all. There is what I believe the lock symbol for this just next to the charge indicator (top right). It is an arrowed circle showing a locked padlock. How can I get it to turn again please. I've tried just about everything in 'Settings' but to no avail. It is difficult to use the narrow keyboard so really would appreciate help from the experts. Thank you very much.