How to change a stroke to a fill?

I have a logo made from strokes and fills. It would be more easy to change the colours of the logo if all the elements would be fills.

So: how to make a stroke a fill?

(If I remember right it should be possible. If I have a 5 pixel stroke, it would become a 5 pixels wide fill. I just don't know / remember how to do it).

Thank's!

Johnny