I made some visual changes to my form by modifying the file formmain.min.css in /gravityforms/css/ but everytime there is an update i have to reupload my modified version of the file to fix it.
Is there another place to make that change so it doesn’t get overwritten each time there is an update?
Do not edit the Gravity Forms core files. They will be overwritten with each update. That goes for other plugins and WordPress as well.
You should add your own custom CSS via the appearance customizer (Appearance > Customize > Additional CSS) or via your child theme stylesheet.
If you are removing Gravity Forms CSS, I recommend disabling Gravity Forms CSS altogether (on the main Forms > Settings page “Output CSS”) and then adding in your own custom styles via the methods I listed above.