The U.S. Flag Code suggests that when a flag has served its useful purpose, “it should be destroyed, preferably by burning.” For individual citizens, this should be done discreetly so the act of destruction is not perceived as a protest or desecration.
Many American Legion posts conduct disposal ceremonies of unserviceable flags, especially on Flag Day (June 14). Such ceremonies are particularly dignified and solemn occasions for the retirement of unserviceable flags.
Take your old flags to your local American Legion post. They will be happy to retire your flags in their next disposal ceremony.