Upgrading to XGP Ultimate deleting currently installed apps with standard subscription?

Xgu doesnt affect your games it only affwcta your subscription

Yes. Anytime you add Ultimate to a standard Gold/Game Pass subscription, it will upgrade to Ultimate. Just make sure you're current subscription is definitely over before adding Gold.

Correct.

Yes, you can do the upgrade again as long as you let your current subscription end first. Once it's completely ended you can add a standard Gold and then upgrade to Ultimate again. Otherwise, if you have Ultimate, you can still add standard Gold and it will
extend the subscription, but not at the 1:1 ratio.

Make sure you are on 1903 win10 version (type winver on search).If not download windows update assistant and follow the steps to update windows.

Download and use Xbox beta app

Login with your account you have upgraded to xgp ultimate

Enjoy XGP Ultimate

It worked as intended. In order to get a refund you would have had to cancel the Standard subscription before upgrading to ultimate. You don't get a refund or discount when upgrading. Once you upgraded, the Standard subscription would have been cancelled and upgrading to Ultimate in addition to the Ultimate you purchased. So you would only get a refund for the Ultimate.