when you type your message, click on "go advanced"
you will see a preview, and then below your edit box
you will also see a manage attachment button.
click on that, a "pick a file from your hard drive" box appears to locate your file/s.
to remove, click the same manage attachments button, or go to the sidebar in your "my apug" page and
click on attachments and pick/choose the ones you want to remove.
if you can't remember what they are you can click on thumbnails for a instant reminder
have fun !