Cannot Change Existing Logo in a Theme

Hi everyone

I’m having trouble changing the logo on the website https://www.jwdoherty.com
The new logo has the following text in it, JWD Fabrication & Machining.

I have searched the forums, but could not find many posts where the solution had been resolved, and where it was resolved in a couple of cases, they were not valid for me.

I have tried the following, none of them seemed to work
1. Using FTP to replace old logo file with new logo file, kept the name same. – Old logo still shows.
2. Uploaded new file to same folder with a different name. Changed the URL to the logo in the Header.php file in the theme [It was the only location where I could find reference to the logo]. Result – Old logo was not being shown, but the new logo could not be detected.
3. Added the URL for the logo into the CSS file – No change, old logo still showed.

Any other suggestions or help would be great!

Many thanks!