Unfortunately there is no way to change the setting in a GUI at the moment so you will have to get out your trusty command line interface and do it manually.
To change the way Ubuntu Budgie displays your Desktop Background you will need to enter one of the following commands depending on how you would like it displayed.
gsettings set org.gnome.desktop.background picture-options ‘none’
gsettings set org.gnome.desktop.background picture-options ‘wallpaper’
gsettings set org.gnome.desktop.background picture-options ‘centered’
gsettings set org.gnome.desktop.background picture-options ‘scaled’
gsettings set org.gnome.desktop.background picture-options ‘stretched’
gsettings set org.gnome.desktop.background picture-options ‘zoom’
gsettings set org.gnome.desktop.background picture-options ‘spanned’
And to reset back to the default setting for Budgie use this command:
gsettings reset org.gnome.desktop.background picture-options