On the lead record, click Edit in the lower left-hand corner, scroll down to the “Lead Owner” and select the new salesperson’s name from the drop down.  Click Save & Close.

lead record

To find all of the leads that belong to one salesperson (in the event of terminated employment) simply isolate “All Leads” in the Business Directory and add the “Owned By” column.

owned by column

You can then “Show Filters” in the upper right-hand corner.  This allows you to enter the particular salesperson in the “Owned By” column to filter only that salesperson’s leads as seen in the third image.  You can now change ownership of all leads listed to the new salesperson.

owned by filter