Customizing the colour theme and logo of Portal (using Community edition ) to suit the look and feel of our organization?

Though, I have read a few posts on how to achieve this using Community Edition of Bonitasoft, yet I have not been very successful in committing the changes. Every time we re-login from within Bonita Studio, we get the original BonitaSoft theme.

Kindly direct me on how to proceed with this in the Community Edition of the software?