To archive an itinerary first choose the itinerary on the Trips page that you wish to archive. Once you click the itinerary, on the right-hand side you will see four different options: Edit, Preview, Copy and Archive.
Press the button Archive to remove the trip from your Trips list!
You will find all of your archived trips under Archived on the left side of your Trips page. When you need to restore any archived trips, press Archived, choose the trip you want to restore and again you will be given four different options to choose from: Edit, Preview, Copy and, this time, Unarchive. Press the Unarchive button to add the trip back into your list of Trips.