Attachment can be deleted from your experiments in several ways:

1. From the experiment page, directly from the file itself, by clicking on the arrow next to each file and selecting 'delete':

 2. By accessing to the attachment page from the dashboard:

Click on the "x" icon that appears next to each attachment.

 3. From the experiment page, when the attachment is an image added to a section, by clicking the trash bin icon:

4. From the Knowledgebase module > image bank page. Find your image, open it and delete with the 'more' menu: