Please see the links below, and also note that you will need to invoke the A-GPS command before invoking the position request command in your application. And if you have the GNSS module attached, then select your gpio pins carefully because there is an issue when using the lower range gpio pins for A-GPS and the GNSS module simultaneously. You should also look into RTK positioning since you will have everything you need except for the software to calculate the RTK position. That is if you need sub cm accuracy. Good luck with your project, and if you haven't found this already, I hope it helps.
Ublox Leon AT command manual.
http://www.u-blox.com/images/downloads/Product_Docs/u-blox_AT_Commands_Manual_(WLS-SW-11000).pdf
The site I found the file.
http://www.u-blox.com/en/download/documents-a-resources/leon-modules-resources.html