Dear Jean-Christophe Ducoin,
If you want your logo on the full width, please log in administrator, go to Extensions -> Template Manager, edit sj health template. Please see on Layout Settings what the file in Select Layout field (example: main-left-right.xml).
Then, open FTP, please go to yoursite/templates/sj_health/layouts and open the file above (example: main-left-right.xml) and find:
<position class="span2" data-mobile="" data-normal="span3" data-tablet="span4" data-stablet="span4" type="feature">@logo</position>
=>
<position class="span12" data-mobile="" data-normal="span12" data-tablet="span12" data-stablet="span12" type="feature">@logo</position>
Thanks