With your Permanent.org account, you can create and join an unlimited number of archives. 

To switch from your current archive to a different archive, navigate to your account menu in the top right corner of your workspace, then click Archives.

A new window will appear that lists all of the archives that you own or are a member of along with your access role for each archive. Find the archive you wish to switch to, then click it. 

The archive that you have selected will open. You can see which archive you are currently working in by looking at the archive information on the left side of the workspace.