Head over to Admin > Manage brands > Basic styling.
We'd recommend uploading a logo image with 400x200 dimensions to appear crisper, especially when viewed on mobile.
JPEG, GIF, and PNG file types are accepted.
The logo will be applied to all of the surveys in your account. If you need to use a different logo on another survey, you can create another brand and upload a different image. This feature is only available for users on the Pro plan. 😉