as far as I know there are no current videos about how to update/upgrade.
If you have ftp and know how to use it then there is nothing a video will help you with.
it is very basic.
1. go to your board admin panel, turn off the board.
2. make a backup of the database from the admin panel
3. connect to your hosting ftp using a ftp program like filezilla
4. dowload all the files/folders of your phpBB to your computer where you can find them.
5. read and follow the instructions about how to update/upgrade.
follow those instructions exactly and in order. do not do anything not in those instructions and do
everything that is in those instructions and you will be fine.
If you have any problem, stop, do not continue , then come back here to ask for help.
be sure to describe exactly what you have done and exactly what happens etc.