Edit sidebar template bit and change it:
{{if $adsForceSidebar OR ( \IPS\core\Advertisement::loadByLocation( 'ad_sidebar' ) AND ( ( isset( \IPS\Output::i()->sidebar['contextual'] ) && trim( \IPS\Output::i()->sidebar['contextual'] ) !== '' ) OR ( isset( \IPS\Output::i()->sidebar['widgets']['sidebar'] ) && \count( \IPS\Output::i()->sidebar['widgets']['sidebar'] ) ) ) )}}
<div data-role='sidebarAd'>
{advertisement="ad_sidebar"}
</div>
<br><br>
{{endif}}
{template="widgetContainer" group="global" app="core" params="'sidebar', 'vertical'"}
To:
{template="widgetContainer" group="global" app="core" params="'sidebar', 'vertical'"}
<br><br>
{{if $adsForceSidebar OR ( \IPS\core\Advertisement::loadByLocation( 'ad_sidebar' ) AND ( ( isset( \IPS\Output::i()->sidebar['contextual'] ) && trim( \IPS\Output::i()->sidebar['contextual'] ) !== '' ) OR ( isset( \IPS\Output::i()->sidebar['widgets']['sidebar'] ) && \count( \IPS\Output::i()->sidebar['widgets']['sidebar'] ) ) ) )}}
<div data-role='sidebarAd'>
{advertisement="ad_sidebar"}
</div>
{{endif}}
This operation change the location of sidebar ads from top to bottom.