Under Customize > Site Identity you can specify basic site information.
Let's review every option in details.
The logo is an image such as a corporate symbol. You can either remove or change it according to your needs.
To change logo silly click to "Change Logo" to open the Media Library. Then you can select an image from it or upload the new image from Upload Files tab and click the "Select" button at the bottom right.
Further options allow you to adjust the logo height, text and description.
