Using the background eraser

Choose a picture like a tree with leaves or anything that you want to
delete the background. The background has to be different colors than
the foreground part you want to keep or it won't work. Open in
Photoshop.

Choose whatever you want to replace the background with and layer it
between two layers of the foreground subject.

Choose background eraser and set it to the second choice on the
top--sample once. Hover you mouse to read that.

Click on one color at a time and do NOT lift your mouse until you've
erased that color (eg, blue). Then do the next color, eg white.
(blue sky, white clouds.)

When all the background is erased in this manner, the new background
becomes visible. You can move in close for more detailed erasing if
desired. The advantage of this is you can easily erase all the sky
behind a whole tree full of leaves with a few passes. It's cleaner
than using the magic wand.

I can see a couple small spots I missed but I don't have time to go back and catch them right now.