Extending XBee Range

Hi,

I have a couple of XBee 2mW Wire Antenna - Series 2 modules (https://www.sparkfun.com/products/10414) at my disposal. I am interested in analyzing the methods for extending the range of data transfer between the modules.

I am not really familiar with antennas. Is there an antenna which would extend the range?

Would making or purchasing a high gain antenna like yagi work and if yes, where could I fin the dimensions for making one?

Also is there a way of using another antenna without unsoldering the one on the module?