If it is a Background layer,
Easiest way is to double-click on the locked layer in the Layers panel.
A dialog will open up giving you options. When you are done setting them, clicking OK makes it a floating or unlocked layer.
If it is a floating layer that has been locked,the lock icon at the top of the layers panel will unlock the selected layer.
Check below link .
You can click on lock icon on the Locak panel, just above the layer in layers panel to unlock the layer.