Hi welcome to IcyPhoenix,
I have moved your question out of the release thread because that one is for new release announcements, bug reports and "thank you" messages.
Please post any questions where you thread is located now in the future, thanks in advance
So, I can't find ANYWHERE on the net how to upgrade a style. Nowhere!
Then you haven't used the search here or even at phpbb.com, neither did you try to use google I guess
If you have no modification made to the original style.. then yes you can simply upload the new style files and overwrite the old.
Ofcourse you should always make a backup incase anything goes wrong!
If you have modifications build in.. then you need to compare the changed files and modify arround them, the unchanged files can be uploaded without this work.
(a list of changed files for every single release can be found in the contrib folder)
PS.. don't forget the language files may need updating too if you have added a custom pack.
TIP: for comparing two files and find differences easilly you could use WinMerge (free)
Greetings and goodluck,
...Joshua203