When looking for reports that have been Scheduled to be emailed to your Users, you'll need to be logged in as the System Administrator User.
Step 1: Unschedule the Report or Dashboard
Navigate to the Reports Tab
One easy way to tell if a Report or Dashboard is Scheduled to run is by looking for a checkmark in the Scheduled Column. The column Header looks like this: 
When you see a checkmark, the Report or Dashboard is scheduled to be run, refreshed and possibly emailed to your Users.
Click on the Name of the Report or Dashboard you want to Unschedule.
If you are un-scheduling a Report, click the Arrow on the Run Report Button and choose Schedule Future Runs:
If you are un-scheduling a Dashboard, click the Arrow on the Refresh Button and choose Schedule Refresh:
Next click either Unschedule Report, or Unschedule Dashboard
Step 2: Delete any Scheduled Jobs
Navigate to Setup
From the Setup menu, use the Quick Find search bar and search the words Scheduled Jobs.
Click 'Create New View' and add a filter where the 'Type' is equal to 'Report Run' and another filter where the 'Type' is equal to 'Dashboard Refresh'.
From there, click on Add Filter Logic that says '1 OR 2'. (See screenshot example below)
Look for Job Names that match the Report or Dashboard you've Unscheduled.
Click 'Del' to Delete any Scheduled Jobs you do not want to Run.
You're Done!