I can't change video format!

[Rabotnik]

This is driving me crazy!
I need to edit some videos on VirtualDub but all my videos are VLC media file. I tried changing extension from .avi to .mp4 to .flv and many others; then i noticed those are, actually, what i said... extensions not formats, so i think that must be the problem. I'm not really sure if VLC is a video format that i could change using any format converter... i'm not sure what it IS! but i really really need to edit those videos, is a project for college. I tried uninstalling VLC but files kept as VLC. Now i installed it again. I don't know what to do.

I need help so much.
Thanks to every answering.