Tip request : Unwrapping

Hi guys.

I’m one of those users that only gets the chance to use blender on a project about once a year so every now and then get stuck on something.

I have a scanned 3d model with texture. The scanning process returns a texture image that’s a total mess, just faces randomly laid out on a grid. I’m sure there’s a simple-enough process where I can mark seams on the object and unwrap the texture to a new, neat image file.

I found a really good tutorial on unwrapping, but how can I do it while preserving the original texture?