I saw in some videos that you could access other classes' editor through tabs on top of the screen, how do you get that? I am running an old version on Greenfoot so that may be the case.
Yes, that may be the case. Only the newer versions of Greenfoot uses tabbing. I cannot, without investigating, say how far back it goes, but older versions create a window for each class to be edited. In newer versions, there is an option to move a tab to a new window.