Trying to make my site look more official… Thumbnails?

Here’s my site: http://www.monsterworm.com

So, I’m really new to WordPress, but I was just wondering: how should I go about centering the thumbnails on my index page? That’s the only things that’s really giving me trouble right now, but I can’t seem to figure out where I should go to do this. I’ve tried going through the HTML editor on the WordPress dashboard, but for some reason, when I go to: Appearance-Editor-Main Index Template, I only get the following message: “Why hello there, Sparky. Whatcha doin’ here.” It might be helpful for you to know that I’m using Headway 1.7 Beta 4.

Someone already suggested:

When you insert the image there are options to align the it: None, Left, Right, and Center. It looks like Right is selected as a default at the moment.

You’ll find these immediately above the size options.

However, I’ve tried to re-upload the featured image and select center, but there are two buttons on the Edit Post Webpress page (Left and Right) which seem to override this selection. Not sure what to do about this or if it has to do with the theme that I am using (Headway 1.7 Beta4).

Thanks for any and all help. Look forward to hearing from you.