Photoshop can be a very complex tool, so if you are new to Photoshop or maybe its just been awhile here is a quick tip on unlocking PS layers. There are several different ways you can unlock a layer.
This one is fairly simple, just select the layer you wish to unlock, right click over it and select duplicate (hot-key: ctrl+j). Now you have a completely editable unlocked layer.
Second: Lock Menu
Again select your locked layer and now look at the top of your layers window for the lock menu and click the lock icon.
Third: Throw it away
After you have your locked layer selected click and drag the lock on the layer to the trashcan on the bottom of your layers window.