Example for 1366×768.
1. Shutdown VM
2. Navigate to C:\Program Files\Oracle\VirtualBox\
3. Shift + Right-Click > Open command window here
4. Run command VBoxManage.exe setextradata “Windows 8 RTM Evaluation” CustomVideoMode1 1366x768x32
5. Start VM
6. Launch Desktop, Right-Click > Screen Resolution
7. Choose 1366 x 768
