**First Method:**("recommended")

Install the [Analytics Database Manager][1]

 - When Analytics Database Manager is installed, access the application from the Sitecore
   launchpad.
 - Go on the "REMOVE OLD DATA" tab, select the desired options and click start.

**Second Method:**

 - Delete your MongoDB Databases related to the Sitecore instance.
 - Replace the Reporting Database with a clean copy of the corresponding Sitecore version or use the **__DeleteAllReportingData**  stored procedure in /Programmability/Stored Procedures .

[![enter image description here][2]][2]

 - Restart your Sitecore Instance.

  [1]: https://marketplace.sitecore.net/en/Modules/Analytics_Database_Manager.aspx
  [2]: https://i.sstatic.net/Fpzad.png