Anyone from the project team can delete an attachment.
To delete an attachment:
  1. Open the Projects panel and select a project
  2. Find the task and click on it's name. The task card will open
  3. Go to tab
  4. Here you can find all the task's "Attachments"
  5. Click the cross to the right of the attachment you want to remove and confirm deletion
A deleted attachment cannot be recovered (but if it was something very important, please contact our support, we will try to help you).