Hi Shan,
We have not yet added the interface to change your email in RStudio Cloud. However, there is a way to do it. The same RStudio login that you use with RStudio Cloud is shared with shinyapps.io, another online service provided by RStudio. To update your email, go to http://www.shinyapps.io and login, then go to the Account / Profile and press the Update Profile button. The changes you make there will apply to your RStudio Cloud account as well.