There should be an "erase" or "delete" option for each image when you are actually viewing it on the camera screen --- look for a button with a recycle bin icon on it --- press that, then choose 'OK' to confirm.
Go through each picture one-by-one and do the above.
You might even be able to connect the camera to PC with a data cable, view all the picture files together in a window and zap 'em all in one go.