Visit the project properties by clicking on the gear icon.
In the project properties, you will find an Archive Project button. Clicking on it will archive the project. Clicking on it again will unarchive it.
To view archived projects, select Archived from the drop-down menu in the top left corner of the screen in the Projects page.
To restore the Archived Project, click on the gear icon to access the project properties. Scroll down then click on Unarchive Project.
Note: Only project admins can archive the project.