How can I revert back to wp 4.2?

Hello,

My website updated to wp 4.3 (currently automatically updated to 4.3.1), and my current theme apparently doesn’t support it. Which seems to have the effect that updates I make to the portfolio doesn’t show on the site, although the site works fine othewise. I have been in contact with the theme’s support and that seems to be the problem since everything should be in order for them to show.

Is there a way I can go back to 4.2, and how do i do that?
I have paid for my theme and don’t really want to buy a new one and remake my website because of this.