[SOLVED] screen only 640x480 - how to change

I'm trying Zorin to see if I can use it at work or recommend to others for Windows replacement while retaining the Windows feel. Just installed Zorin-os-9-core-32.iso into a VirtualBox with Host Windows 7 Pro.

I've tried poking about in the forums and online and can't find how to get more options for Screen Resolution than the default 640x480 Zorin gives me in the System Settings.

I've installed approx. a half-dozen other *nix variants without having this issue so a little stumped why Zorin gets stuck.

And before you point me at a thread about SIS stuff I have no idea what SIS is or stands for and don't see any reference to it in my Device Manager.
The Host unit is Windows 7 Pro running on a Dell Latitude 6410/6420 (not sure which exactly) with Intel HD 3000 graphics listed as the Display Adapter.
My host unit has both it's built in laptop screen and an additional 22" VGA screen attached.

I even tried changing the default VirtualBox settings for Video to offer a "hint" of a larger screen resolution than the default 640x480.

I don't mind hitting the terminal and pasting some "sudo" commands etc, or modifying some startup script, but frankly this should work out of the box if you want more easy adoption of your "flavor".

So - any suggestions in my case?
Thanks

I finally got this to work. Turns out I had to:
1) In VirtualBox insert the Guest Additions ISO file
2) When it showed up on the desktop as a mounted disc in Zorin open a terminal window
3) CD your way to /media/username/VBoxAdditions(etc) (whatever the ISO file name is)
4) Then SUDO the .run program for linux like this: sudo ./VBoxAdditions(etc).run
5) Enter your password to okay the program to run
6) When install is complete, just reboot Zorin and BAM! the screen works like a champ, auto resizing as I drag the VM from one screen to another too!
7) BONUS: and now the Zorin VM isn't capturing my mouse either so I can freely move between my host and guest!

PROBLEM SOLVED (now the real question is why couldn't I find this solution anywhere?! Surely I'm not the only one to have run into this...)

HI, thanks for sharing your solution - I have played with Zorin Lite inside of Deepin without any issues - I normally have to get the 'addons' package for USB wireless dongle pass through anyway, so guess why I have not encountered this issue. 120 bue jewels to you sir! 60 for solving your own issue and another 60 for sharing!

Thanks - it's strange to me though that I had to install the guest additions this way in Zorin - I never had to do that on any other flavor I'd tried so far. But, now I'm a tad smarter so that's good too!