Moving from HTTP to HTTPS

I am trying to move across to HTTPS and am having an issue with mixed content in theme_mods_sydney to get the “green padlock” in Chrome etc. I can see the front page header images start with http in theme_mods_sydney in my SQL database. I have tried to change this to https and I have removed the domain name to start with //. When doing either of these, the site returns to the default theme state.

Is there something I am missing or doing wrong here?

Thanks
Alex

Can’t test this right now but there isn’t much we can do about it unfortunately. The option for image uploading in the Customizer is a core WP option. The theme isn’t defining it.
What you could do is check out slider.php, copy the sydney_slider_template() function (it’s pluggable) and overwrite it from a child theme. Then hardcode your images directly without protocol.