Reformatting references once their in Word

Let’s say that I submitted a paper to Nature, and then it was rejected, and I want to submit it to another, such as the Journal of Cognitive Science.  How can I change the format of the references in the word document without manually deleting and reinserting each one (because there are over 300 references)?  

Thanks! 

Reformatting your manuscript using different output style?

I respectfully suggest to go through this training.

http://www.endnote.com/training/