1. You can find all the changes
in this topic.2. If you modified one of the built-in screensets then it will be overwritten. You should always make a copy first with another name and modify that instead of the original. Here are some steps to save your work:
In 1.2111 there was only the old screenset which has the pictures in the Flashscreen\BMP\Defaultscreenset directory and the screenset file Screens\Defaultscreenset.ssf. Create a directory, e.g. Flashscreen\BMP\MyScreen and copy all the images from Defaultscreenset. Go to the Screens directory and make a copy of Defaultscreenset.ssf as MyScreen.ssf. Now open your profile with Notepad and change the second line from "mainscreenfilename=Defaultscreenset" to "mainscreenfilename=MyScreen". Now if you start UCCNC you should see the same as before, but now you can update the program. To be safe, make a full copy of the UCCNC directory before updating and you'll have a backup if anything goes wrong.