Rooting the phone will erase all of your data.
All described operations you are doing at your own risk.
If want saves your data do a backup before start.
The battery should be at least 50% charged before starting.
Rooting Sony Phone Tutorial
Turn on SONY Xperia NX SO-02D phone and connect to WiFi network.
Go to Settings --> Security --> turn on unknown sources
Open Chrome browser and type address download.hardreset.info
Open directory sony them root and download aplication HardReset.info_kingroot.apk