What is the difference between G3,G4,and G5? How does an inmate transition between them?

The higher the number, the higher the security level of the prison. G5 is maximum security. Inmates are designated by the department of corrections after they are sentenced. After an inmate has begun his sentence, there are intervals of behavioral and advancement analysis done. This is used to determine if the inmate is showing signs of accepting incarceration and working on improving themselves. This improvement is rewarded by lowering their security level status and making them eligible for downward transfer, also know as "working your way down".