This means your current logo in the Global brand settings is too large. You can upload a smaller logo. But if you want to keep it, you can still upload a new logo from the theme editor. To do this, please follow the steps below:
In the content editor, click onto your header and open it in global content editor (Website header module).
Then go to Website header > Logo and set the Override default logo toggle on.
Upload your logo and set the size values as you wish.
Once you change this setting, you must click Apply Changes first, and then click Publish to X assets button at the top right corner. This way it will take effect on your site.