How do you change the backround in a game?

I want to learn how to change the backround of a game is because i am making this game and i want the time of day to pass from day to evening to night.

www.roblox.com/Day-Night-Cycle-Script-item?id=562993

Put that into workspace, make sure to understand it before you use it. Maybe even rewrite it.

If you want to change the background completely, try inserting a Skybox: http://web.roblox.com/My/Sets.aspx?id=38438