Y720 tower top panel access

Does anyone know how to open the Top Panel of Y720 Tower. I am looking to fix a fan on the top but dont know how to remove the plastic top frame. One of the promo videos says use a tool on the buttons on the top inside. But dont know which ones. I saw vidoes on how to open the front panel, side pane, removing PSU etc. but the top panel, where we have the power button is also detachable from the case is what I understand. Kindly help.