Christina, this would be a good question for @Getting Started with CA Agile Central and the answer is simple. Projects have a state (Open or Closed) and if an admin sets the project state to Closed then it will no longer appear in the workspace dropdowns. Please note that the contents of Closed projects are no longer indexed for Search so you'll want to be sure that you're really done with one before you close it. If you determine later that you need something from a closed project then it's extremely easy to reopen it. Hope that helps.