1. Navigate to the DM you would like to leave

2. Select DM details by either right-clicking (desktop)  or long-pressing (mobile) on the DM in your DM list

3. Click on the name of the DM in the top-left corner once you're already inside of that DM, or click on the profile picture(s) of those in the DM in the top-right corner

 

3. Select "Leave"