Removing the glue from teeth due to permanent retainer?

I would NOT recommend removing any adhesive (glue) from your old retainer at home as this could damage your teeth. I think your best option is to find an orthodontist who can remove the glue for you and discuss options for a new retainer (there are many different kinds of retainers).  Long term studies have shown that everyone's teeth (even those who have never had their teeth straightened) have a tendency to crowd as we age (especially the bottom front teeth).  The only way to prevent this is regular wear of a retainer.  While there may be some cost associated with a new retainer, it will definitely be less expensive than having to undergo treatment again in the future when your teeth move!