Move navigation to below the header

Yes, first create a Child Theme.

Thanks I’ve done that. Is it in the php I have to make a change?

Yes, copy header.php from your theme and paste it into your Child Theme directory.

Try replacing all of your Child Theme header.php code with this;
https://pastebin.com/0g7n7KPe

That’s done it thanks. I’ll study both headers to see what the difference is.
Thanks very much for your help.

As a matter of interest, what is the Raw Paste Data beneath the header php code on the pastebin page?

That’s the same code without any fancy colours.

Great help Andrew, once again, many thanks.