Click on the gear icon in the main menu and then on the name of your company.
To insert the logo of your company, click on the upload icon inside the box in the top right, and save.
To cancel the logo, right click on it (or hold, on the tablet), select Delete and save.
Same applies for the image cover, which is on the lower right corner under Cover image.
While the logo is seen on documents, the cover image is the picture of your company seen by other users in Sengerio.