if I already have a residence address registered with the DMV
You are not required to change it when you change your email address, but you can change your residence address if you wish.
I need details of the Document number
Document number. The document number is 8 or 10 characters, and is printed in the lower right corner of your DMV photo document, or on the back for document issues after January 29, 2014, The 8 character format is all numerical.