You can easily stop individual ads, audiences, or all activity in your Top, Middle or Bottom of the Funnel campaigns.
From your dashboard, click "edit campaign" on your Top, Middle or Bottom Funnel.
On the next screen you can edit settings by clicking the three dots (...) beside the different elements of the dashboard.
Turn off campaign:
To turn off all activity in the entire campaign, click the three dots to the right of the top headline and a menu will appear like the one below.
Click Turn off and all activity will be turned off in this campaign.
Turn off audience:
Hover with your mouse over the audience you want to turn off and three dots will appear (...).
Click the dots and the below menu will appear. Click Turn off, and all ads targeting that audience will be turned off.
Turn off ad set:
If you only want to turn off an ad set within an audience, click the audience that contains the ad you want to turn off. Then hover on the ad you want to turn off, three dots will appear (...). Click the three dots and select Turn off from the menu.