To recover archived leads you first must have leads archived, Sales > Lead Management. 

Select the Leads in the Lead Summary with the checkmarks on the left of the lead. Then click the Action button at the top, and select Archive Leads.

The system will ask if you are sure you want to archive these leads.

When archiving leads you can add notes for why are are being archived. For instance, they may be very old leads that are not active anymore or killed off because they do not want to buy a franchise anymore.

Once Archived, the leads are taken out of the Sales pipeline. These leads can still be seen by going to Search and selecting Archived Leads.

If you want to restore the Archived Leads again check the boxes for the corresponding leads and select the button Move to Active Leads.

Again the system will ask you if you want to add a note as to why these leads are being unarchived.

Now the leads are available in the sales pipeline again.