1. Open a constituent record.
  2. From the Constituent menu, select Copy Preferred to Alternate. 
OR
  1. Open the address.
  2. Select Address from the Drop down menu.
  3. Select Copy Preferred to Alternate.
Note: Changing an address to alternate address will not break the sharing.

To set a Business Rule that uses a default Address Type when copying Preferred to Alternate, see How to copy a preferred address to alternate and default the address type