How do I change from scaled mode in VirtualBox?

To exit scaled mode in VirtualBox, simply press the Host key + C again.

Here's a breakdown and some additional information:

Exiting Scaled Mode

Keyboard Shortcut: The easiest way to toggle in and out of scaled mode is by pressing the designated Host key (usually Right Ctrl) and the C key simultaneously. So, to leave scaled mode, just repeat that same key combination.

While the keyboard shortcut is the quickest method, you can also use the VirtualBox menu:

Access the View Menu: Within the Virtual Machine window, locate the "View" menu at the top.
Select Scaled Mode: If you are currently in scaled mode, the "Scaled Mode" option in the "View" menu will be checked. Clicking it will uncheck it and return you to normal (non-scaled) mode.

To reiterate:

Method	Action
Keyboard	Press Host key + C
VirtualBox Menu	View -> Scaled Mode (toggle option)