The chip in my dog how do i fix the info?

the girl that gave me the dog is on my side. she does not want her father to come get the dog from me beacuse she gave him to me. she said she will do whatever it takes to help mme keep the dog she had giving me a month ago. the dog has a chip in him incase he gets lost it has her name & info on it. i need to switch it to mine asap. how do i do that???