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
By default Site branding block will be placed in Site branding region. If its not, place it.
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 site name and site slogan of your website from:
Home Administration Configuration System Basic site settings
How To change default logo image
Replace logo.png image present in theme folder with your own logo image.
Make sure, name of logo image is logo.png
Home Administration Appearance Appearance settings
Uncheck option Use the logo supplied by the theme.
Click Browse... button to upload new logo. Click Save configuration button after selecting new logo image.