How to transfer stub-article into my sandbox 

Hello Dr. Scott , I have a quick question for you. I'm writing my article on Aspergillus terrus and it's already a stub article on Wikipedia. I want to expand it but I'm not sure if I should make changes on the article's edit page or whether I should move the existing information into my sandbox (as an external link) where I can then continue the writing process. I've referred back to the Wiki Training for Students but unfortunately I'm still confused. 
Thanks,in advance, for your help!