You can set up and later on change your organisation's logo. It will be visible in the top left corner of the site together with the name of your organisation and when switching to it. For example:
To set up the logo, go to Organisations > Basic Information tab. First, click on Edit information on the Available Actions panel. Now you can update the logo by simply clicking on the Update company logo box. You will be asked to browse your computer's folders to choose the right file. Please note that it should be either in .jpg or .png format and its size should be smaller than 1 MB. After uploading the logo, click on Update Information to save the changes.
Please remember that this option might be limited to certain roles (Owner, Manager) and service-levels only.