The easiest way to change the registration is to contact the company that made the chip. The chip number and contact information for the company should have been provided to you when the animal was microchipped (or adopted). Most companies have an online registration update available through their webpage, just search by the brand name of the chip (HomeAgain, 24PetWatch, AVID, ResQ...). If, however, you no longer have the paperwork from the original registration, and thus don't know the brand of chip or the chip number, you should take the pet to a shelter or veterinary clinic (pretty well any of them should have a scanner) to have the chip read. They will tell you the chip number and brand, and should be able to provide you with contact information for the chip company.
Some companies charge a minimal fee for changing registration (AVID, for instance, charges $6), others don't. If you are changing only address/phone number, that should be all you have to do. If you are changing owner though, you may be required to send a signed statement to the company saying that you sold/gave/released the pet to the new owner. This may seem like a hassle, but the idea behind it is to prevent someone from stealing a pet and just changing the registration to their own name.
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The easiest way to change the registration is to contact the company that made the chip. The chip number and contact information for the company should have been provided to you when the animal was microchipped (or adopted). Most companies have an online registration update available through their webpage, just search by the brand name of the chip (HomeAgain, 24PetWatch, AVID, ResQ...).
If, however, you no longer have the paperwork from the original registration, and thus don't know the brand of chip or the chip number, you should take the pet to a shelter or veterinary clinic (pretty well any of them should have a scanner) to have the chip read. They will tell you the chip number and brand, and should be able to provide you with contact information for the chip company.
Some companies charge a minimal fee for changing registration (AVID, for instance, charges $6), others don't. If you are changing only address/phone number, that should be all you have to do. If you are changing owner though, you may be required to send a signed statement to the company saying that you sold/gave/released the pet to the new owner. This may seem like a hassle, but the idea behind it is to prevent someone from stealing a pet and just changing the registration to their own name.