The Currency Exchange is a powerful tool! 

Once your businesses are booming, you can exchange cash for Mega Bucks! Use the arrows to adjust how much you are willing to cash in for currency! 

Where is the Currency Exchange? 

In the AdVenture menu! Tap on the Settings Menu > AdVentures > Exchange. 

Is there a limit to how many Mega Bucks you can collect? 

Technically no, but as you reach end-game it becomes increasingly more difficult to earn enough cash to collect an extra Megabuck. The amount of cash required to exchange increases with every Megabuck you collect so it will come to a stand still.