Sometimes when you first power on your Ubuntu Virtual machine (or any similar VM), the window size and resolution are quite small.
Here is a short tip on how to increase the size of the window.
First in you virtual machine, click on Settings after you have selected the Ubuntu VM :
This will open up the window below (make sure you click on the Display icon on the top):
Now as shown above, modify the value of the scale factor. Once done, click OK.
Now start you Ubuntu VM :
You will notice that the screen size has changed.