You will find a star counter at the top of the screen that represents your prestige level. When you complete all the upgrades in a specific working area, you get a new star and the possibility of ranking it up. 

This action also allows you to expand your offices and departments, as well as it will unlock new upgrades.
 
*Read carefully all the requirements needed to expand your offices and departments in their descriptions!
 
 
Remember to be patient! If you see a feature blocked, you just need to work a little bit harder to win more cases.
 
**If you reached the vault's max level and there are some pending upgrades, please take in mind that new content updates will bring more upgrades, so you will be able to advance further in the game. The team is working on it!