Hi,

I think you did some customization with style. By default the size of sidebar is defined in the block file, for example:

Open the file and you would see the following code:

<div class="t3-sidebar t3-sidebar-1 col-xs-6  col-md-3  col-md-pull-6 <?php $this->_c($vars['sidebar1']) ?>">

	<jdoc:include type="modules" name="<?php $this->_p($vars['sidebar1']) ?>" style="T3Xhtml" />

</div>

In the code, the sidebar-1 width is set to col-md-3. The same for sidebar-2. You can change the col-md-3 to col-md-2 or 4, however, please make sure you have to change the width of other section: main content section and sidebar-2. The total col of the page is 12 (follow bootstrap 3 grid system).

If you want to keep the same grid system, but change to width of the sidebar with CSS, you can add the following CSS rules to the file: templates/t3_bs3_blank/css/custom.css

.t3-sidebar-1 {

    width: 200px;

}

Regards.