You can always do it at the guitar shops. I'm not sure if they charge for service now but for my understanding in the past, if you purchase a set of strings, they would do it for you free of charge. See them do it once and you'll be able to do it yourself, it's pretty simple.
I'm not a guitarist myself but I do know how to restring a guitar so it shouldn't be too difficult for you to pick it up. That said, please do double check with the guitarists on this forum regarding the restring service at shops!