Hide Submenus

Hello, I am using the Cathe Flames theme (www.triopetra.com.gr), and i would appreciate some help. At the "Menu" bar, i have some fields, and for example at one field (Guests' reviews) i don't want the submenus to appear there, as a scroll down menu. Only when one goes into the main field (Guests' reviews) and they click on each submenu, only then they can be directed to the submenu. How can i hide the submenus from appearing at the menu bar, as a scroll down manu? Thank you in advance!