How to change default mail address for installing apps in windows 8 web store app

How to change default mail address for installing apps in windows 8 web
store app

Can any one help "How to change default mail address for access windows
store apps in windows 8 web store app". I didn't find any option "Sign in
with different user".
Please see the image to understand...(Sorry i don't have points to post
image) http://i.stack.imgur.com/B0egx.png
Thanks
Satish