You can change the details and settings of a menu here.
Menu Location - Sella supports 2 menus: Primary Menu and Sidebar Menu
Top primary menu - Choose which menu in the Menus would like to use as the primary menu. Secondary menu in left sidebar - Choose which menu in the Menus would like to use as the sidebar menu.
Top primary menu - Choose which menu in the Menus would like to use as the primary menu.
Secondary menu in left sidebar - Choose which menu in the Menus would like to use as the sidebar menu.
Menus - These are the menus made by you. You can make/add a new menu or delete it here.
Note
You can also do the same thing by following Menu Setup instructions in Widgets & Menu > Menu > Menu Setup.