Many thanks.

I understand that is a Linux Command and it will reset file owner as the default owner.

Unfortunately  I don't know how to run a linux command.

How do I run it?

I have ftp access to my webserver via  filezilla, plus I have access to my hosts console.  I have googled it, there are millions of websites offering to help but they all go on and on about what is in the linux command, not how and where you execute it.

In short: there is no "one answer fits all".

Specifically some sudo command is ill-advised if the setup constellation isn't known and neither is the user's expertise.

Regarding directory and file permissions, it really depends on which user owns the files and as which user the web server runs. In hosting packages that usually is the same web server user and group as it was the one creating files when installing the software; things can be more complicated if a dedicated ftp user owns the files. During an upgrade (performed by the web server) the then writing user obviously must have write permissions.

Iff your web server (e.g. user www-data) owns the files and also the files' primary group is the web server's group (i.e. the above example's ownership is www-data:www-data) and you (as a different user) never edit files from the command line (or by other means not involving the web server user) then directory permissions 750 and file permissions 640 are perfectly fine.

If you edit files from the command line and belong to the primary group but are not the owner of the files then 770 and 660 may be needed.

There can be other constellations, for example where you and the web server are the same primary user (i.e. in a chroot jail), in which case even 700 and 600 may be sufficient.

If xx7 and xx6 are needed that's a sign for a questionable setup.

But things may be setup differently using ACLs that go beyond primary user,group,others permissions. If in doubt and unless you manage your own server always ask your hosting provider.