When you have used menus in lots of pages and it is required to change the menu for some pages, the Menu Replacement feature is provided. You can choose the menu that you want to replace.
By clicking on the ‘options’ icon of the menu, you will get an option of Replace Menu. 
By clicking on the ‘Replace Menu’, you will get the Menu Replacement popup from where you can select the Menu that you want to Replace with it. So, you will not be required to navigate to the individual pages and update the menu. 
You will get all the pages in which the selected menu is used. Select the required pages that you want to replace the menu for.
By clicking on the Replace button, the pages will be replaced by the selected menu.