Hello,
I’m confused a little bit. If you don’t like content that you have in the 4th column go to Appearance > Widgets > add the necessary widget into 4 Footer column widget area (tags or any other or remove widget at all to make it empty). If you want to add any content to prefooter use Prefooter widget area and Static Block option, don’t forget to enable Visual Composer for the Static Blocks to be able to use page builder for the block.
If you are not able to create the necessary block then provide me admin panel access and screenshot what exactly should be in every area and every column.
Regards