The front part is just secured by 2 metal clamps that can be disengaged by pulling upward while also pushing the cushion towards the rear (position yourself squatting facing the rear). The cushion should now be pulled out completely.
Pero, kung hindi mo matanggal despite ma disengage yung clamps sa harap, baka merong bolt in between the seat cushion and the sandalan. you can remove this by an extended socket wrench. try to feel for this bolt by putting your fingers in the crevice between the seat cusion and the back. good luck.