After an item is created you can always change the order of the documents attached to it.
Go to the item screen for the subject meeting.
The third tab is the Attachments tab
The Attachments tab has two parts: the list of documents currently attached to the item on the left, and a viewport on the right.
Grab any attachment the list of attachment on the left, drag it and drop it where you want it. The order is updated immediately upon dropping.