Ceiling fans require more support than the suspended ceiling can give. We recommend using an electrical box designed for ceiling fan applications attached directly to the joists or cross support.
Start by removing enough of the tiles to create an adequate work space above. You will probably have to remove at least two or three tiles where the fan will be located.
Install the electrical box to support the ceiling fan as it is designed. To make sure the box is at the right height, hold it to match the thickness of the ceiling tile below the ceiling grid. Before the fan body is installed, cut your ceiling tile to fit around the electrical box, and put it in position.