MT Template Help

So, I’ve received several complaints that my individual index archive page is too wide. I would fix this, but it turns out that this might require my thinking about HOW to fix it, and I don’t want to do that. So, I’m hoping somebody will tell me how exactly, so I don’t have to think about it. Thank you.

[UPDATE: I meant the individual archive pages, the page where you go when you click the permalink. Thanks, Kipp, for you help. Sorry for being so dumb that I ask for the wrong thing.]