Recommended sizes:
For a site logo – 173×40 px (or 346×80 px for retina), the width is not fixed and can be different.
For a site icon – 512×512 px.
1) Go to Appearance – Customize – Site Identity.
2) Click on the Select logo button. Upload and select (also, once selected, click the Skip Cropping button) a logo image.
3) Click on the Select site icon button. Upload and select a site icon (favicon) image.
4) Publish the changes.
