The top panel is not removeable. It is identical to a lot of other cases.
Normally the fans in the top panel should be installed before installing the motherboard and cpu heatsink. You may have to remove them to get access to the interior of the top panel.
The fans are attached to the interior surface of the top panel. Place the fans against the interior of the top panel. Line up the screw holes. Insert screws in the screw holes on the exterior of the top panel. Secure the fans to the top panel.
You would be better off not removing the case fan at the bottom front of the case. The bottom front to top rear airflow is the classic configuration. You could replace the fan with a fan that has a higher rpm and airflow.