Facing error to update deasil theme from 2.10 to 3

I am trying to upgrade deasil theme but I got following error
Fatal error : Cannot redeclare deasil_menu_cart() (previously declared in /home/egtou/public_html/wp-content/themes/deasil/mega-menu/cart-menu.php:3) in /home/egtou/public_html/wp-content/plugins/deasil-core/mega-menu/cart-menu.php on line 104

I could not activate plugin desil core


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