How do you change a dog's name?

We just got Missie (our first puppy together) at the aspca... she is wonderful... but my husband's previous dog's name was Missie and Missie was everything to him... he said she was born in his hand and they were inseparable for 14 years. its been 2 1/2 years since the first Missie and I know he loves this Missie, but I can tell its hard for him to call her that. she will be one january 1. can i even change her name?