Calling any other blogger who uses this blogger.com site

If any other blogger can help me here I'd appreciate it. The width of this template I use isn't wide enough. I think it is limted to 660 pixels and I want it wider, like near 800.  Where in the heck do I change this is the Edit HTML option? 

If that's not possible then can I setup a banner ad on the left hand side. Might as well fill up this dead space.