If you're going to switch his name I'd do it sooner rather than later. And I agree with pp's about calling him the new name and his old name (like hyphenated) for awhile, not just switching cold turkey.
I say this because when I taught in a 3yo room at an early childhood center a little boy named Tommy suddenly came to school saying "My name is Vinnie now". He was adopted and apparently his father decided - three years after adopting him - that his son HAD to have his name. Vinnie Jr. withdrew and became sullen and sulking and visibly upset every single time we called him Vinnie. His father was such a control freak, demanding that he knew best and that any reference to Tommy was stricly prohibited. It made us sick. At the age of 3 he had come to know his name as part of his identity, and he was so confused for so long.
Sooner rather than later, really, if you want to switch names, and gradually. I think my one year old would be alright with a name change, because she has a million different nicknames from so many people and answers to all of them. I can totally see a one year old accepting a gradual name change!