Xbee AT mode or API mode

I know Arduino can monitor the inputs , like temperature sensor , then send the readings back to PC user through USB. Where the PC connects to Xbee-Coordinator through USB Port and its adapter for Xbee. Then it will talk to another XBee-Router which connects to Arduino (ATMEL- ATMEGA328P)

but i do not know the Xbee setting for send the reading on arduino.

My setup is as follows:

Transmitter:
Arduino UNO with Xbee Shield (iteadstudio Version 1.1)
Tiny RTC DS1307 Shield with DS18B20 Temp Sensor
Arduino Powered using Laptop’s USB port
Xbee S1

Laptop:
Xbee S1connected to FT232RL Tiny Breakout – Foca (iteadstudio Version 2.2)

My Xbee Configurations:
ArduinoXBEE
(XB24, 802.15.4, 10E8)
ID = 1111
DH = 13A200
DL = 4081B858
SH = 13A200
SL = 4081B859
BD = 9600

LaptopXBEE
(XB24, 802.15.4, 10E8)
ID = 1111
DH = 13A200
DL = 4081B859
SH = 13A200
SL = 4081B858
BD = 9600

if i use the AT mode, also i just want to send the temperature data XX.XX send from one side(Arduino) to other side(Laptop)

According to the xbee 802.15.4 configurations, what is the MY setting?

Or this function is not available on AT mode?
i find Xbee have a API mode for transmit the data too, but i dont know how to set the Xbee 802.15.4( i only find the example for Xbee Serial 2, they set the coordinator or router API on function set during XCTU. )