Fatal Error Message – suco theme

Hi I am using the Suco wordpress theme. I have been using it for some time. I just went to make some revisions to the website. When I click on the “customize” link I get the following error message. It won’t allow me to go the the Customize area of my site.

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 3072 bytes) in /home/brazosmg/public_html/wp-admin/includes/class-wp-list-table.php on line 1203

Any idea what this means?

Website is: http://www.brazosmg.com/

Thanks for your help,
saranee