Welcome to Android Central! 4.1.2 was the last official version from Samsung: Firmware for Samsung GT-I8262 - SamMobile. You'd have to ask them why they didn't update it further. You might be able to find higher versions as custom ROMs, but you'd have to root the phone first.
Or find a CyanogenMod ROM that's built on a later version of Android. (There's an installer on the CyanogenMod Installation site, but you'll probably have to go back to version 11 or 10 for hat phone.)