Simple yet cant find how to do it ? Change Site Logo for top left menu

Hi, What i thought should be quite simple thing is giving me some trouble.

Quite simply i wish to change the logo on my site, I would like to change
this one -
with this one -

I tried
1) replacing old one in FTP with the updated one (same name) - hasn't worked
2) Changed in the Theme Customisation screenshot - - hasn't worked
3) checked Simple CSS & style.css cant find it there either.

im probably missing something very obvious or maybe not hope someone can help me out?

Support Access is open
Domain -

Please dont post any brand related information/ screenshots or domain links as i have had issues with google caching this information and linking it to their google searches of my site ... very bad for brand... please use temporary image upload / tiny url / pastebin etc to mask this information.