Hello,
I just want to know how could i change the logo to my own ? and also please tell me how to change favicon also.
All helps are much appreciated !!
MiaB doesn’t have a favicon. 
There is an issue on Github opened to add the favicon but someone with the appropriate knowledge needs to turn it into a pull request.
Regarding the logo … the project has one but I do not see it on the box itself … which logo are you referring to? the Roundcube logo?
You can add a favicon to your site by placing a favicon.ico file in the web directory of your site.
I don’t recall the default config, but for me that is /home/user-data/www/mail.example.com/favicon.ico and all of my browsers seem to be able to find it.
It is useful for being able to quickly find the tab with MiaB in it.