Pardon if this is obvious but I ask just to be certain.
I would use the following steps.
1) Transfer [lineage-13.0-20170304-UNOFFICIAL-land.zip] and [firmware-update-11.02.zip] to device internal storage
2)reboot device into recovery (in my case twrp)
3) install the rom zip the same way I initially installed CM13
4) install firmware update via same method as step 3
5) reboot to system
I assume I wont need to re-flash GApps
please advise if my steps are correct.
again sorry if this is obvious, this is pretty much my first time ever using custom OS on a phone so im somewhat stupid in this regard.