Removing, substituting, filtering and otherwise changing a background in a photo can all be done quite easily in Adobe Photoshop CC. The hardest part is separating the background from the foreground objects, but using the Color Range select tool can make this process much more convenient. If you're replacing one background with another, you can just delete the background pixels. If you just want to alter the background, use a duplicate layer to separate foreground objects from the photo's background.
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Replacing a Background
Click the small Lock icon located in the Background layer of the Layers panel. After you do this, the layer is renamed "Layer 0." Unlike a locked background layer, Layer 0 supports transparency, so you can delete pixels without them being replaced with a solid color.
Erase the background from the photo using the Eraser Tool. Another way to erase is to use the Lasso Tool to encircle the background, then press Delete.
Use Color Range to remove most, if not all, of the background. Click the Select menu and then click Color Range. Click a background color in the photo and then drag the Fuzziness slider so that as much of the background is visible in the preview as possible, while the foreground objects are black. Click OK.
Press Delete if none of the foreground is selected. Otherwise, use the Eraser Tool to delete the selected background pixels.
Zoom in and out of the photo to verify you have deleted all of the background. Clean up any missed pixels with the Eraser Tool. If you accidentally deleted part of the foreground objects, press Alt-Ctrl-Z as many times as you need to go back.
Locate an image that has the background you want in Photoshop. Drag it onto the canvas and press Enter to place it. In the Layers panel, Drag the new layer below Layer 0 to make it the new background.
Adjust the background as needed. Beyond resizing or scaling the background, which you can do using the options under the Edit menu, you may need to blur a background using a blur filter from the Filter menu.
Adjusting a Background
Drag the Background layer onto the New Layer icon at the bottom of the Layers panel. Remove the photo's background from the top layer the same way you would when replacing a background. To make your work easier to see, hide the bottom layer by clicking its Eye icon, then make it visible again when you're finished.
Make any changes to the bottom layer, without affecting the foreground objects still visible in the top layer. A good way to make these changes while you experiment with different effects is to insert a layer between them by selecting a Fill Layer or an Adjustment Layer from the Layers panel and then dragging this layer between your two photo layers. If you change your mind, you can just delete the adjustment layer or make it invisible without having to go back and redo your work.
Select Filter Gallery from the Filter menu while the bottom layer in the Layers panel is select. Select a filter that suits your photo and adjust it as needed.