N5 NOVA 
RK3318 20190912
N6 MAX RK3399 20190610
N5MAX 2GB RAM Android9.0 20190702
N5MAX 4GB RAM Android9.0 20190702
N5MAX 2GB RAM Android8.1 2GB RAM 20190716
N5MAX 4GB RAM Android8.1 4GB RAM 20190716
IRON+ DDR4 DDR4 20181226
IRON+ DDR3 DDR3 20180717
IRON S905X 20180727
N5 2.4Gwifi with Drop down menu bar S905X 20190510
N5 2.4G/5Gwifi with Drop down menu bar S905X 20190522
N5 2.4Gwifi without Drop down menu bar S905X 20190628
N5 2.4G/5Gwifi without Drop down menu bar S905X 20190628
C300 S905D 20181221
C300 Pro S912 20181221
C400 Plus DDR4 S912 20190108
C400 Plus DDR3 S912 20181120
Page about : How to upgrade N5 MAX
Video about : How to upgrade N5 NOVA
Page about : How to upgrade via USB Burning Tool
Video about: How to upgrade via USB Burning Tool
Video about: How to upgrade RK3399 N6MAX
USB Burning Tool 
Page about : How to upgrade via TF card
TF Card Tool
If you don't have AtoA cable and TF card,or don't want to upgrade via USB Buring tool or TF card.
You can upgrade via OTA .
Download the .ZIP file,uncompress it.
there are two file,one file(.img) is for USB Burning tool upgrade,one firle(.zip, this file do not uncompress) is for OTA upgrade
If you want to upgrade via OTA
Just copy the OTA version firmware .zip file (do not uncompress) onto a USB disk, turn on the box,
select the NewOTAupgrade>>local upgrade>>wipe all data, it can upgrade automatically.
Notice: now only C300,C300PRO,C400PLUS have the OTA firmware version,the other model will release later