It seems there's a bit of a communication flaw here.
Bramblestar, please specify. Are you wanting to change the background of the room where it says "Studio Pixel presents..."? Or are you wanting to change the background on the main menu where you select "New" or "Load"? I'd assume the latter, but your terminology of "title screen" is better applied to the former. If you're talking the title screen which is shown before you're taken to the main menu, Bombchu and Randolf are right. If you're talking the main menu, then Dunc and MagicDoors are right.