Just noticed your message, i'm currently upgrading to 4.1 as I write.
As Terry Says, i tend to use 'Save As' at each stage and create a milestone i can go back to, so for example my saved files may look like this;
newsong_Mix vocal tweaks
However the autosave function is here;
I've never bothered with it, so probably check out the Presonus forums for more information.
All the best