Where can I download free softwear to I can change a movie background?

Could anyone tell me plz where can I download a free softwear to I can change a movie background??

Plz I need a free softwear to download for:

Changing a movie background??

where can I download for free???

Making slid show with music on background??

changing the background? do you mean sound or video? changing the background video would be quite complex and require sophisticated software.

If you have windows, and just want to change the sound, the free version of Windows Movie Maker that comes with Windows should be able to do that. Likewise on a Mac iMovie should be able to do that too. Changing the nackground soundtrack is easy, changing the video background is hard.