Moto G LTE (1st) gen - where are system version updates downloaded? My personal phone is a Moto G LTE 1st gen (XT1045 - peregrine). At some point it stopped receiving network signal, so I re-installed Android 5.1 using a zip from XDA. I also rooted the phone.

Now my system version is 23.21.37.peregrine_retus.abc.xyz, whatever. I got a notification that I can install a new version, and I accidentally downloaded it. The problem is that I don't want to install it, but I keep getting reminders and I always postone. Where can I find the downloaded file to delete it? I didn't find anything in \cache in the internal storage. I looked in a lot of places using ES File Explorer, but I couldn't find the file that would be used for the update.
Location is /cache usually, but for explorers even with root enabled cannot browse certain locations (not sure if you are using systemless root, in which case ES doesn't get root permissions )

Booting into recovery and using TWRP file manager (Advanced tab) allows you to browse and delete the update file as confirmed by OP

Regarding the other problem of update installation messages popping up, one way is to identify and "freeze* those /system components responsible for searching updates. You would need to search for indicative names. On my device (Moto X Play), freezin 
configupdater,SEpolicy update,Motorola update services did the trick. I use ROM Toolbox to freeze . Other alternatives like Titanium Backup should also work