Change IP address of a Virtual Machine running linux ubuntu on windows 8?

Instead of setting a static IP like others suggested, I simply enabled "Bridged Adapter Mode" under "Network Connections", and then this made it such that each new virtual machine I made automatically had a new IP address.

If you click "Bridged Adapter Mode" and it doesn't have any choices (i.e.the only option is "Not Selected"), then you can simply go to "Network Connections" on your host machine, right-click on the network, click "properties", then "Install", then "Service", then "Add", then Install "VirtualBox Bridged Networking Driver". After doing so (and restarting my computer), it started giving me different IP addresses for each new virtual machine.