To upload a new logo, log into your Smart Flow web account, go to Settings, then Document Management, in the top section you are given an option to upload an image: 

Click Upload Image, and upload the image from your computer. 

NOTE: For better appearance in forms, it is recommended to use a logo with the landscape orientation, when the width is at least two times bigger than the height. In order to save space on the documents/forms, the logo will be resized automatically to not exceed maximum high on the page, thus portrait oriented logos (as well as square or round shape) will appear too small on the document and will not use space effectively. Resize the logo to fit approximately 7: 3 proportions (width: height). 

There after, the image will appear on your form!