How do I create more disk space?

Hello everyone
I’m taking a block chain course via the linux foundation. I’m a newbie. They did a horrible job on instructing how to set up the ubuntu and docker and had to pretty much learn how to install it on my own. One of the things they DIDN’T tell you is how much disk space to allocate. So I underestimated and ran out of space. I’m using ubuntu 16.04 via Oracle virtual box. Anyone have any tips or will I have to muddle through the youtubes again?