How do i unlock my sd card

There is a slider on the left hand side of an SD card which sets the card to Locked (lower position) or Unlocked (higher position - i.e. towards the top of the SD card). The first step is to check the position of this slider.

Note that the position of the slider does not affect the SD card in any way - it trips a switch inside the camera (or other SD reader). The slider MUST be in the upper position or the camera will say Card Locked - so if the slider has fallen off (they are very fragile!) the camera will assume it is in the Locked position.