To change the mega menu please follow below steps.

Step -1: Login to your admin panel go to Extension -> Module. Please see the screenshot below.

Step -2:  Now go to Shopme Mega Menu - Menu Management.  Please see the screenshot below.

Step -3: Here you can create a new menu or you can edit the existing one. Please see the screenshot below.

Step -4: In the same page below you will find  Content type to select Please select  category here and add the category  that you have created. Please see the screenshot below.

Step -5: Save