K2634 Quad Triac card control

hi all,
The K2634 Quad Triac card can switch 4 loads of 24-230VAC at up to 4amps.
The inputs are opto-isolated, & the manual states:
"for use with regular open cololector output and a control voltage of 9 to 15VDC.
Arduino outputs are 5VDC, 40mA. hmmm.
Each of the K2634 inputs has a resistor labeled "Rx" and should be 820 ohms for 9 - 15v, Rx should be 1.8Kohms for a 24VDC control.
So, can I simply then lower the value of Rx to 400 ohms and then connect an Arduino control pin directly to this card?
Or must I build some type of transistor circuit to drive the inputs of the K2634?
Thanks in advance for any advice for a newbie.
Cheers

can I simply then lower the value of Rx to 400 ohms and then connect an Arduino control pin directly to this card?

NO

must I build some type of transistor circuit to drive the inputs of the K2634?

YES

But it is simple, just a transistor with its base connected to the arduino output through a 1K resistor. Emitter to ground, collector to the - pin of your card. I can't tell from the schematic if the RX resistors are fitted. If they are then connect them directly to the Vin supplying your arduino or connect an external 9 to 12 v power supply and make the grounds common.

any advice for a newbie.

Don't mess with mains on at least your fist four projects.