Interesting question, I am curious why you wish to do this.

If its because you want to install 0.4 directly, those isos arent ready yet

However! you can upgrade to 0.4 after going to 0.3.1.

If you are not sure, or are afraid of losing files, etc... back them up on a large storage usb.

That being said, if that is not your reason, feel free to let me know.

I can try to help if needed, I have not tested 0.3.1 in a while to install from scratch

Its pretty easy to do, depending on your goal.  Follow the guide, and it should be successful.  But do so as strictly as possible. Also, if you intend to do full disk encryption, with or without /root, 
Scroll way down:

you need to make certain changes to mkinitcpio.conf via the full disk encryption guide, either the one for newbies on this forum, or the libreboot one, in either case though,
there is one change mkinitcpio.conf does not say to make which is crucial or it won't boot:

At the very top non commented MODULES line, you must remove the apostrophes after the = sign, or everything else won't work in booting.

And if you make this mistake, I will try to tell you how to chroot into the system, but try to avoid making that mistake.

IF NOT, you should very much be able to easily, do both! 

I wish you the best on your goal. Hope this helps.