Step 1: Log into your Drupal 7 Admin panel.
Step 2: Using the top menu area, click on the Appearance option.
Step 3: This will bring up the themes page where it lists all themes installed within Drupal 7. Locate the Settings tab at the upper right corner of the screen and click it.
Step 4: This brings you to the main Appearance page. You will see Global Settings followed by the name of all enabled themes as a top menu bar. To set the option globally, click on the Global Settings option. To set it for a particular theme, simply click on the name of the desired theme. This will bring you to the settings page.
Step 5: Find the Toggle Display list on this page. Find the Main Menu setting. Simply click the checkbox to disable it.
Step 6: Click on the Save Configuration button at the bottom of the page to save the change.