1. Log in to your dashboard--> Design- -> Edit HTML

2. Search "Ctrl+F" and find </head> and above it add:

<b:if cond='data:blog.pageType == &quot;static_page&quot;'>  
<style type='text/css'>
.art-content-layout .art-sidebar1,.art-footer-body {display:none;}

In your template the sidebar and footer may have different name (exemple: art-sidebar; art-footer; content-layout .sidebar1; footer etc) , in this case replace the colored lines with the name find in your template.

Also if you have 2 sidebars in the template just add the name of the second sidebar (exemple: .art-content-layout .art-sidebar2) after .art-content-layout .art-sidebar1 followed by a ","

3. If you want to hide the sidebar and footer only in a specific page replace the orange line in the code with:

<b:if cond='data:blog.pageType == &quot;The_Particular_Page_Url&quot;'>  

 Replace The_Particular_Page_Url with the url of your static page.

4. Save the template and you're done.

DEMO: See the Forum and Content pages in my site.