Roof vent upgrade?

Wasn't sure where to post this... Has anyone upgraded their old, non-powered, roof vent to a powered version? Wondering how difficult it might be...

IIRC, the newer TM's come with a powered vent anyway. Could it be that it uses the same size opening as the old models? I was thinking I could maybe steal power from the lighting circuit up there.

Any advice for me??

Thanks,

Steve