How to enable boost mode XBee Pro S2C

I am using a XBee Pro S2C and need to transmit data to about 1.5 km away. I tested the module at a place far from people and other obstacles but range was about 50 or 75 meters. So I thought I should be using boost mode and my questions are:

(I am asking about effects on range in all “does it matter” questions.)

  1. How can I enable boost mode?
  2. Does it matter which protocol I use? (Digimesh, Zigbee, 802.15.4)
  3. Does it matter which serial interface I use? (SPI, UART)
  4. Does it matter which serial interface protocol I use? (Transparent, API)

I am sorry if answers are something very easy to find. I am totally new to XBee.
Thanks in advance.

Boots mode is enabled by default. It is not going to effect the range by that much. It only enables about 1 to 2 db more in output.

No it does not matter which protocol or interface you use.

What I would suggest is looking at the article that covers Range.