You can start with the upgrade docs.
They are updated now within the version 7 upgrade So there is no need to read the txt file within the zip file:
https://www.ubbcentral.com/doc_upgrade7.php
Then before you upgrade you should backup your site:
Using a ftp program such as Filezilla for the scripts and Cpanel for the database


Blue Man Group
There is no such thing as stupid questions. Just stupid answers