When you select a virtual machine from the list in the VirtualBox Manager window, you will see a summary of that machine's settings on the right.
Clicking on Settings displays a window, where you can configure many of the properties of the selected VM. But be careful when changing VM settings. It is possible to change all VM settings after installing a guest OS, but certain changes might prevent a guest OS from functioning correctly if done after installation.
The Settings button is disabled while a VM is either in the Running or Saved state. This is because the Settings dialog enables you to change fundamental characteristics of the virtual machine that is created for your guest OS. For example, the guest OS may not perform well if half of its memory is taken away. As a result, if the Settings button is disabled, shut down the current VM first.
Oracle VM VirtualBox provides a wide range of parameters that can be changed for a virtual machine. The various settings that can be changed in the Settings window are described in detail in Chapter 3, Configuring Virtual Machines. Even more parameters are available when using the VBoxManage command line interface. See Chapter 7, VBoxManage.