According to page 17 of the controller (SSD1289) datasheet (provided in a zip file from the link you mentioned), the controller can be addressed in different parallel widths. Further, you can also use serial bus to use even less IO lines.
You can move the display from the pcb, the white casing, exposing the flex print beneath. On this you will find R4 populated while R5 is not. Move R4 to R5 position and it will be 8 bit device. Use D0-D7