ACP>Look & Feel>your_skin>Templates>Board Index>boardIndexTemplate

Find:

<div id='index_stats' class='right clearfix' <if test="sidebarclosed2:IPSCookie::get('hide_sidebar') == '1'">style='display: none'</if>>
<foreach loop="side_blocks:$side_blocks as $block">
{$block}
</foreach>
</div>
</if>

<div id='categories' class='<if test="nosidebar:IPSCookie::get('hide_sidebar') == '1' || !$this->templateVars['sidebar_enabled']">no_sidebar< /if> clearfix'>

Change it to:

<div id='index_stats' class='left clearfix' <if test="sidebarclosed2:IPSCookie::get('hide_sidebar') == '1'">style='display: none'</if>>
<foreach loop="side_blocks:$side_blocks as $block">
{$block}
</foreach>
</div>
</if>

<div id='categories' class='<if test="nosidebar:IPSCookie::get('hide_sidebar') == '1' || !$this->templateVars['sidebar_enabled']">no_sidebar< /if>right clearfix'>

Now, we need to move toggle button, which closes and opens sidebar, from the right to the left.

Go ACP>Look & Feel>your_skin>CSS tab>ipb_styles.css

Find:

.sidebar_toggle {
text-align: right;
padding: 0px 3px;
height: 20px;
right: 15px;
position: absolute;
-moz-outline: 0;

and change position value from absolute to left.

Hope this helps