First, if you do not know how to download its iso and load it in the virtualbox, please refer to tutorial at this url: https://roboticsbackend.com/install-raspbian-desktop-on-a-virtual-machine-virtualbox/
And once you have it setup and running then you will need to install virtualbox guest additions as describe here:
First mount it to the virtual OS
- Click on Devices menu and then Insert Guest Additional CD Image
- This will popup. Click Ok
- Right click on VBox _GAs… and Open in Terminal
- Execute this below command with sudo meaning you elevated yourself as privileged user.
- sudo bash VBoxLinuxAdditions.run
- Hit enter and wait till it complete
- Next we need to edit /etc/X11/app-defaults/Editres
- Execute below command
- sudo mousepad /etc/X11/app-default/Editres
- Next give it a desired resolution we like. in my case I gave 1000 width/height.
