How to design a day and night process
You will be able to make a day process by this example, It will teach you to convert a day to night by animation.
Open Picture: Capture any nature image to modify.
Ellipse Tool: Select Ellipse tool (U key) and set color "f2f2d2", draw a circle shape like the sun as given below.
Levels: Select your background layer and go to Image Menu > Adjustment > Levels and increase level as given below.
Draw again sun and increase levels status as done up.
Apply same upper steps until you don't have this image.
Image Ready: Click bottom of the tool bar, you will directly reach in the Image Ready. You will find a frame in the animation window.
Adjustment: You have to adjust all the layers by the frame in the animation window to make a complete animation as I have done here.
Save File: Now save your file, go to File menu > Save optimized.