You can upload your logo image by navigating to the Appearance->Customize->Site Identity. If the logo is not uploaded, then your site name will be used.
Please, follow the steps below to upload your logo:
Step 1 – Login to your WordPress Dashboard.
Step 2 – Go to Appearance->Customize->Site Identity.
Step 3 – Upload a Logo. Size doesn’t matter but if you want to make logo retina use a big size ( our logo is 80px x 43px ).
Step 4 – Set the width size for your logo ( default 300 ).
Step 5 – Upload your favicon – should be a 512px x 512px Png image.