Hello and welcome to the forum @Hi58!
I'm afraid that the Xperia Z2 D6502 does not support LTE (4G) networks. You can see the supported networks listed below:
UMTS HSPA+ 850 (Band V), 900 (Band VIII), 1700 (Band IV),
1900 (Band II), 2100 (Band I) MHz
GSM GPRS/EDGE 850, 900, 1800, 1900 MHz
This information is directly from the white paper for the device, you can find the full document on this link: http://www-support-downloads.sonymobile.com/d6503/whitepaper_EN_D6502_D6503_D6543_4.pdf
Note that the reason that that your phone does not support LTE networks is due to a hardware limitation. No form of software update will unfortunately not be able to enable this.
I'm sorry for any trouble this may cause for you, let me know if there is anything else you are wondering about!
