Hello,
How can I change the logo size? I want to decrease the logo, because I think is too big. Thanks. 
I hope you are well today and thank you for your question.
In the theme there isn’t any restriction on the logo size so you can set any logo image having any size in the theme customizer Site Identity settings. In short you have to resize the logo image before uploading and setting it as logo in the theme settings.
Best Regards,
Movin