Within Survey Settings/Details/Publish Survey section, there is the option to 'Display logo on survey' and if checked an additional field 'Select File' is displayed:
Use the select file to navigate to the image and click on 'open'. Please note: valid file formats for logo's include PNG, JPG, or GIF
Then click on the upload button to successfully apply the logo to the survey. A 'Success' message is displayed once the upload is complete.
Please note: use the 'Preview' feature on the Build Questions page to review how the logo is displayed:
NOTE: The Survey needs to be in edit mode before adding the Logo. The Survey should have been saved with basic settings and then edited, to add a Logo.