As you advance in the game, your barbershop will include more and more objects. Some of them are decoration, but others will need to be upgraded if you want to improve your performance. 

Tap on the magnifier icon, and small blue arrows will appear over those objects that could be upgraded with in-game money. Then, you only need to select those objects where you want to invest your earnings. We strongly recommend you to read their descriptions carefully to know which is the best option according to your strategy.