can i change the background of a video after iv already made it ?

[Abel]

Try making a "blue screen " at home and place a tree in front of it and record for the length of time you need then use a video editing software like Sony Vegas (free trial I think) and there is a feature on there that lets you layer video on top of each other. Don't know if it would work for sure. I made a video like that but I recorded people in front of the blue screen and then added a second video layer behind them later. To make the screen I bought a cheap blue plastic table cloth. Wasn't perfect but it served its purpose.