Duplicate the background layer, work on the background copy layer, shut off the visibility of the background layer by clicking on the eye icon. That way, if you need to start over, delete the newly generated layers,
and you are back to square one.
Go to Enhance menu>Adjust lighting>Brightness/contrast and increase the contrast
Use the Magnetic lasso tool to select the background within the confines of the key ring, and hit delete on the keyboard.
Use the same tool to select the lock and its housing. You should see marching ants once the selection if complete.
Press CTRL+J to put the selection on its own layer.
Open a blank layer between the background copy layer and layer 1, and fill the layer with white. You should have 4 layers: Background layer (shut off), Background copy layer, Layer 2 (white), Layer1 with the object at the top.