Network unlocking is not free and costs a lot. Besides, there are no tools available for this procedure. I myself have an Xperia M2 and to unlock it, I must pay almost 60 $ towards the carrier's network or at a local phone shop. Firstly contact Sony and then visit a local phone shop and they should provide additional Help regarding this issue.
You can also ask for directions on the XDA Forums, the mobile phones place to meet: http://forum.xda-developers.com/