How best to lower LED garden light intensity
The best and most economical way is to reduce the voltage of the supply with the small orange screw near the terminals. Outdoor hermetically sealed supply don't have this adjustable screw (potentiometer). In this case replacing the supply may be necessary. It can be cheaper or not more expensive than buying a PWM dimmer. PWM dimmer consume more electricity but are better fit for accessible, user friendly, regularly adjustment. For a one time adjustment, setting a lower voltage is better and more climate friendly (LOL). The change in voltage has to be of the order of 10%. If you replace the supply by a supply with 30% less voltage, it will be too much.
You can reduce voltage safely. But you can't increase it.