You can archive a project from your "My Projects" list. Check out this video to see how:
If you need to UNarchive a project, you can do so by navigating to Projects in the left-side navigation, then "All Projects" in the secondary menu. Once you're on the page that shows you full list of projects, click the checkbox that says "Show Archived" (to the right of the search bar in the page). The page will refresh to show all archived projects. You can then find the archived project you are looking for and click the undo button to the right of it to unarchive it.
**Note: Archived projects will disappear from the left-side navigation bar, however, the project will still show up on reports if you choose and will still be counted towards your total yearly project allotment based on your membership subscription.