I'll help you get that logo replaced without any further issues. Is there a specific error message appearing when you try to upload the new image? Any additional information or screenshots you can supply will help to expedite the troubleshooting.
In the meantime, I recommend replacing the logo in a private window to ensure there are no browser issues holding things up. The steps below will help you accomplish this:
Replacing company logo in a private browsing window
From anywhere in your browser, press the corresponding keyboard shortcut: Chrome: Ctrl+Shift+N Internet Explorer: Ctrl+Shift+P Firefox: Ctrl+Shift+P Safari: Command+Shift+N
Click the Gear icon (⚙), select Account and Settings, and click the logo box on the Company tab. Attempt replacing the image from here.
The private browsing window loads QuickBooks in a way that prevents local cache files from being stored. These cache files are meant to save you time while loading repetitive information in QBO, but can often lead to visual and loading errors. Please let me know if this allows you to replace your company logo without issue. Thanks for bringing your question to the Community, I'll keep an eye out for your response.