The Near smart downlight has a cut-hole diameter of 154mm. The most accurate way of obtaining measurement is to remove your existing downlight and measure the diameter of the ceiling hole.
Alternatively, you may simply measure the outer-diameter of your downlight without removing it, if it is smaller than 154mm, it means that you will need to enlarge the hole by using a wall-board saw.
Most houses in Singapore use a 6 inches downlight or smaller, that's why we opt to manufacture our downlight at 6 inches. It is always easier to enlarge the hole size as compared to covering the hole.