How to manage website logo
You can use Site Name, Site Slogan or Image as your website logo.
How To Use Site Name and Site Slogan or Image as Logo
Home Administration Structure Block layout
Click Configure button of Site branding block.
Select the options that you want to use as logo and click Save block button.
You can set / configure site name and site slogan of your website from:
Home Administration Configuration System Basic site settings
How To change default logo image
Home Administration Appearance Appearance settings
Here you can upload new logo image.