Hello Lois,
Yes, you have to reactivate AVG with the new license number manually. Open AVG Internet Security > My AVG > My Subscription > Select Logout/ Remove license (if you have that option) > Select Enter the license > click OK to reactivate the program.
If you face any difficulties, please provide the screenshot [http://support.avg.com/SupportArticleView?urlname=How-to-create-a-screenshot] of the AVG Subscription Window to assist further.