Compiling Cellbots

Okay, so i have a robot that is controlled by an arduino mega. I also have a bluetooth shield to connect to my android phone. I found this app called cellbots and got it to work with my robot. Then i wanted to modify cellbots(its open source). so i downloaded the source code. I probably could figure out how to modify it and add my own functions to it but how do I compile it into an apk??? Does anyone know how to compile the cellbots source code into an apk?????????? :~

Here's the app: https://play.google.com/store/apps/details?id=com.cellbots&feature=search_result#?t=W251bGwsMSwxLDEsImNvbS5jZWxsYm90cyJd