To change the logo on a system, you need to do this in 2 places, the first area is Administrator > Interfacing - there is a box called company logo delete the old company logo then right (ctrl) click into the field and select insert picture, then select your picture.
The second place that you need to navigate to Administrator > Divisions > Interfacing and do the same as before.

Note: The size of the logo is 158 x 100 px at 72dpi