I have found two ways of getting promoted in this game. To my knowledge, getting promoted only changes the color of your uniform.

1.) In Area 4, go to the place with the waterfall. You should be on the lowest platform. When you get to the edge with the skull and crossbones, swing across. There will be a Comm room there where you will need to use the Green decoder. (You can also tap the message to listen in on a dumb conversation.) Then talk to your superior officer and he will tell you that you have opened Area 16. There are no enemies in Area 16, just one big obstacle course.

2.) The second promotion is when you get to the blue room where you have to swing on the lamp post in Area 11. When you drop down the next hole, instead of swinging on the lights, swing on the ceiling until you get to the red platform. Then pull yourself up and keep going up and swing on that ceiling. Swing to the right and grab the red platform and pull yourself up. Swing on the lamp post and fall into the second hole that you encounter. There will be a Comm room there where you will need the Yellow decoder. (Tap this message for cooking tips.) After speaking to your superior officer you will have opened Area 17. This place is a sewer with many raptor type enemies. Good luck!!