10.14.6 Security Update for MacBookAir will not complete

The 10.14.6 Security Update for MacBookAir will not complete. Internet connection is good. I have tried shutting down and restarting the computer. I keep getting the message that the session has timed out. I go to restart the update and it just stays at 817.9MB of 1.57MB. Then I get the timed out message after a few minutes again. How do I get this update to complete?