Clean up an IAR Microcontroller C project

We have fully working IAR C code for a Nuvoton ARM project which targets several sub devices. We want to tidy the code so that each device only exists in it's particular file. So for example we have files main.c,A.c,B,C.c but at the moment device A is also accessed from main as well as A.c. In short we want the C code tidying. Remote access will be given to the Target device for checking functionality.