Removing Input Fields

You can (and must) design your own class.
Just copy the class you want to customise from /model folter and paste it into /model/custom.
Then do the change you wish in the /model/custom classes : they won't be erased with upgrade.

Unfortunately, if there is a change in the class in a new version, you won't see it, or you'll have to merge your changes in the new class.
But your changes are preserved and never erased.