Some year ago there was the Header Tag plugin which did this easly.
Now Header tag plugin is not in JED and its web site is closed.
I found another free plugin that changes from h2 to h1. I tried it and it seems to work.
Aimy H1 Heading:
https://www.aimy-extensions.com/joomla/h1-heading.html
Among the free extensions you'll find also Aimy No Generator:
https://www.aimy-extensions.com/joomla/no-generator.html
that delets "generator" meta tag from the HTML code.
I hope these information may be usefull to someone.
Thanks
A nice day
Andrew