GP8413 2-Channel 15-bit I2C to 0-5V/10V DAC Module

I am using Arduino UNO and LabView to control ‘GP8413 2-Channel 15-bit I2C to 0-5V/10V DAC Module’.

a. I can control the voltage range by sending 0x77 or 0x55 to register 1. 

Two byte (unsigned 8 bit integer)

1. Register - 0x1 

2. Data- 0x77 or 0x55 (10V and 5V respectively)

b. I can change the voltage output by sending low and high bit of voltage to register 2. 

Three byte (unsigned 8 bit integer)

1. Register - 0x2  

2. Data- Low byte

3. Data - High byte

c. How to change the channel of output voltage?

Which hexagonal byte should I choose to select the channel?

Where should I place that byte in code? Whcih register?