Hi Chantal, sorry for the delay, but I have no notifications from this forum. (if you want to tell me anything about the theme, his page should be the correct place: http://www.emm-gfx.net/2015/12/wordpress-theme-material-for-coders/)
You can name your menus with the name that you want. Just create a menu and select it on the menu place manager.
For example, in my case, I named Material 1 and Material 2 the header and the blog menus, respectively.