My computer is pretty old so I'd really like to have Unity 2D enabled. Does anyone know how to do that? Thanks in advance!
If your computer is old then it is probably defaulting to unity-2d by default - this is called "fallback" mode.
To check that you are using unity-2d use the linked Q&A below.
If you are actually using unity-3d, then you can logout of the live CD, change session to unity 2D and then log back in.
To do this, press the Dash button and search for terminal.
force a logout by typing:
Change the session to "Unity-2D" by pressing the cog button.
Your username is "ubuntu" and there is no password.