[tbworld]

If you can post a link to your board it would help us give you the correct information.

--------------- Added 27 Apr 2014 at 13:52 ---------------
I think this is what you are looking for:

.body_wrapper {
  padding-left: 20px;
  padding-right: 20px;
}

Change the value to your desired padding width and add the code to the bottom of the template "additional.css" in the ACP(Admin Control Panel - admincp) --> Template Manager.

Your template structure may be different, that is why we need a link.