Movable Type guru needed

I just upgraded one of our other blogs, Downtown Tomatoes, from Movable Type 3.2 to 4.12. Attempted to add the Minimalist Green style, but now, as you can see, the templates appear to have no CSS attached to them.

Any MT users out there who can help me fix the site?

It appears the easiest way is to upgrade to mt4 template, but I’m not quite sure how to do this. My mt3 templates are custom.