How to change widget or sidebar width

[webauthor]

I'm sorry if this has already been answered but I can't seem to find a solution. There must be an easy one.

From sidebar.php I've commented out sidebar_right.php so that it looks like this:

<?php include(TEMPLATEPATH."/sidebar_left.php");?>
<?php //include(TEMPLATEPATH."/sidebar_right.php");?>

What I end up with is blank space where sidbar_right.php used to be (see image attached).

What I need to figure out, is how to increase the width of the Categories and Archive widget (which I'm concluding is sidebar_left.php) to take up the space where the Blog and Admin widgets used to be.

I'd then like to add other widgets, like Translation, Videos etc all the same width as they've done on this site:

http://teamwize.com/training/

Any suggestions?

Thanks in advance for your response.