You may delete any collection that you created.
You may not delete a collection which you only have Viewer or Editor sharing permission to.
Steps
1. Go to COLLECTIONS > Manage.
You may click the My tab in order to only see dashboards that you own and can delete.
2. Select the line of the collections to delete.
3. Click Delete.
4. Click Yes.
Example
Go to Collections > Manage.
Click the My tab.
Select New Tables and click Delete.
Click Yes.