Hi Michael Struck,
I am not sure what you want you change since on T3 Blank there are many layout to change.
They are almost the same, though you need to figure out which layout you are using and make change of it.
Please open \templates\[your template]\tpls\blocks\mainbody.php
// Layout configuration
$layout_config = json_decode ('{
"two_sidebars": {
"default" : [ "span6 offset3" , "span3 offset-9" , "span3" ],
"wide" : [],
"xtablet" : [],
"tablet" : [ "span12" , "span6 spanfirst" , "span6" ]
},
"one_sidebar1": {
"default" : [ "span9 pull-right" , "span3" ],
"wide" : [],
"xtablet" : [ "span8 pull-right" , "span4" ],
"tablet" : [ "span12" , "span12 spanfirst" ]
},
"one_sidebar2": {
"default" : [ "span9" , "span3" ],
"wide" : [],
"xtablet" : [ "span8" , "span4" ],
"tablet" : [ "span12" , "span12 spanfirst" ]
},
"no_sidebar": {
"default" : [ "span12" ]
}
}');
Here the configuration for the mainbody layout.
"default" : [ "span6 offset3" , "span3 offset-9" , "span3" ]
It mean, in default state (desktop window), the component will has span6 (width in bootstrap), sidebar-1 will be span3, span 2 will be also span3.
You can change it to "default" : [ "span8 offset2" , "span2 offset-10" , "span2" ], so it will make two sidebar smaller and the main component will be wider
It require some knowledge about bootstrap grid and php to change it.
Regards