Locate the Pathway that contains the Activity you wish to Archive and go into its administration area (see find content in Content Manager if you're unsure how to do this).
Click on the Activities tab on the left.
Tick the box next to the Activity you would like to Archive.
Choose Archive from the Actions dropdown menu.
Click on Confirm in the popup window. 
The Activity will now be Archived but only within the Pathway.
An Administrator will see the Activity listed in the Activities tab of the Pathway and it will be highlighted in grey to indicate its Archived status.
The Activity will still show as active in the Content Manager and Find Learning (if published). To Archive an individual Activity outside of a Pathway, please see the Archiving an Activity guide.