No Logo update possible after latest update on 3.1.5

Hi – I relocated the website of a customer on their proper server.
Therefore it is necessary to re-upload their logo.
This is not working.
I click on upload – the window opens to select the jpg file – I select it and the window closes – but then no further action! No upload – nothing.
I am using Safari as my main browser.
Please inform how I can solve this problem – but customer insists on having the logo at place…
THX for support!
Marion