HTML dummy in need of help

Pooh. I'm HTML clueless, and trying to figure out how to expand the sides of my current template. I might just get a new template - but if I have no idea how to customize the pixel sizes, not having a way to modify the appropriate graphics etc, well I can forget about it.

Why? Simply because I wish to put up bigger pictures - but if I do so, my blog gets messed up.

I guess I'll try to tackle it after I finish my last exam paper. In the meantime, does anyone have any advice?

I tried messing with portions like the following, but to no avail:

/* ---( layout structure )---*/
#wrap { width: 847px; margin: 0 auto; text-align: left; background: url(http://www.blogblog.com/tictac/tile.gif) repeat-y; }
#content { margin-left: 62px; /* to avoid the BMH */ }
#main-content { float: left; width: 460px; margin: 20px 0 0 0; padding: 0; line-height: 1.5em; }
#sidebar { margin: 0 41px 0 547px; padding: 20px 0 0 0; font-size: 85%; line-height: 1.4em; color: #999; background: url(http://www.blogblog.com/tictac/sidebar_bg.gif) no-repeat 0 0; }