For one, you wouldn't be able to select it. If there so then look at your Layers palette. You should see a little padlock icon there.
Padlock.png
All you have to do is to click on it.
If, when you try to select the layer, it selects it as one whole box, then the whole thing is an image and you'll ned a Photo program to edit it. Hopefully it has good resolution for what you are doing.