XBee tools for configuration, example of use:

$ cd python

Start the xbee-serial-terminal.py: 
$ python xbee-serial-terminal.py

Select the baudrate: 

xbee% baudrate 57600

Select the serial port: 
xbee% serial /dev/ttyUSB0 (your serial path may be different!)

Enter AT command mode: 
xbee% +++ 
and wait for OK

Change the power level: 
xbee% ATPL 0

Change to API mode:
xbee% ATAP 2

Change the node id (for a node, not for coordinator): 
xbee% ATMY FFFA

Query a setting, e.g. MY:
xbee% ATMY
reply will appear

Write all the changes, so the XBee remembers them for next time:
xbee% ATWR