You can archive a campaign by scrolling to the far right hand side of the All Campaigns list view and clicking on the Trash Can icon. Note that archiving campaigns will hide it from the All Campaigns list view, but will not delete it. Active campaigns that are archived will continue to run until they are completed or aborted.
Viewing Archived Campaigns
Scroll to the bottom of the All Campaigns page and click the View Archived Campaigns text:
Click on it and the campaign will return to the All Campaign list.