When the product page is displayed your store will - by default - use the "detailed description" of the product. If the detailed description is empty then it will
use the short description.
If, for any reason you need the default description to be the ‘short description’ instead, then you will have to make a change to one of your store template.
The template name to modify is: product.tpl
its full path is:
<store-root-dir>/skin1/customer/main/product.tpl
In order to edit this file, you can access your server by FTP or telnet, or you could use the "edit templates" interface available in your store admin. This
interface can be accessed by clicking on the ‘edit templates’ option in the ’CONTENT MANAGEMENT’ menu section.
The changes to apply. In the product.tpl file find this line:
<tdclass="Descr"style="padding-top: 3px;">{if $product.fulldescr ne ""}{$product.fulldescr}{else}{$product.descr}{/if}</td>
and replace it by this one:
<tdclass="Descr"style="padding-top: 3px;">{if $product.descr ne ""}{$product.descr}{else}{$product.fulldescr}{/if}</td>
Note the strings 'fulldescr' and 'descr' should replace each other.