This photoshop video tutorial shows how to use layers. By using few layers you can change the background.
Disable your original layer after you duplicate it at the beginning of this tutorial.
Remember the layer you are removing the background from is your second layer.
Pay attention which Layers you are working in compared to the video. "Background Layer" has no transparency, so you can't delete the background from it.
At the end layers will be staked in this order.
black & white soft light model
Background (original layer) (turned off)