HOME EDITION - LICENCE EXPIRED

I get LIC Expired message. I have re-registered, GOT THE KEY BUT HOW DO I APPLY THIS KEY to it ANTI VIR XP.
Do I have to re-install or is there a file that I need to run to renew the licence ?
Thanks for UR help.

Right click on avast! tray icon and select About. There you’ll find button to enter the key.

Watch this tutorial Insert Registration Key - Video.