Help Me Upgrade OneFS From 7.2.1.5 to 8.1.2.0 (Production)

Hello guys, I have 8 Nodes , four of them are NL400 and another four are NL410 and another A100 for backups.. what are the procedure to upgrade the OneFS ? what i need to look for before upgrade. what i need to look after upgrade. do i need to upgrade the firmware just for the OneFS or also to all the disks ? maybe to something else ? maybe its just one click and its done, i have no idea... thanks for help