how to adjust virtualbox screen resolution code example

Example 1: virtualbox screen size too small

follow the steps:
It is recommended that you set 128 MB of video memory, as when a video mode with higher resolution is used, more video memory is needed. You can also enable 2D and 3D acceleration.

open cmd:
cd "c:\Program Files\oracle\virtualbox"
VBoxManage setextradata "NAMEOFVM" VBoxInternal2/EfiGraphicsResolution 1920x1080

Example 2: virtualbox fullscreen resolution

Go to the VirtualBox options while in your VM (the same place you went to to install Guest Additions) and select View -> Auto-resize Guest Display. This should automatically set your VM's resolution to the proper screen size.