how to increase resolution of linux virtual box guest

I've got ubuntu installed on virtual box, on a windows7 host

The default resolution for ubuntu is 800 x 600, how can I increase this?

My windows7 resolution is high, this makes my virtual box window very small and difficult to use

On ubuntu, I can't seem to find a way to increase the resolution, I only have choice of 800 x 600

Do I need to install some drivers?

You need to be sure to have the guest additions installed, and to do that it is best to install the dynamic kernel module support (dkms) package first. From a terminal / command prompt:

sudo apt-get install dkms

Once that has been installed, you can mount the guest additions ISO and run the installer script, reboot and you should be able to adjust the resolution, run in seamless mode, etc:

sudo /media/VBOX*/VBoxLinuxAdditions.run

There are some additional ideas and advice given on the Ubuntu StackExchange site:

https://askubuntu.com/questions/3205/higher-screen-resolution-in-virtualbox