I had try to fund information about this on the forum but i wasnt successful.
Is there any way to updaet from 1.4 to 1.5?
An update is not possible.
You must flash the image on the sd card.
You will loose all your playlists and settings.
Also note the thread about testing i2s by michelangeli.
testing-needed-for-i2s-dacs-t1958.html
In 1.5 there is an issue with hires playback over i2s. First post tells you how to fix.
If you have no problems - no need to apply the fix.
/Palle