Do you have any suggestions for me before the upgrade process for EP821 terminal to this version: SIRIUSV400R005C00B353?

Hello,
Please read these precautions:
Precautions
l When upgrading the terminal using the short number in OTA mode, do not change the default user on the eUDC or change the user on the terminal. Otherwise, the short number of the terminal may be changed and the terminal will fail to receive upgrade commands sent to the original short number.

l When upgrading the terminal in OTG mode, perform the upgrade five seconds later after plugging in the OTG cable.

l Since the Direct Boot Mode feature is supported, the previous version of B012 needs to be restored to the factory settings after upgrading to this version.

l You must use the full package when upgrading with OTG or SD card.

l If the terminal has been rooted before the version upgrade, you must use the full package to upgrade. The differential package upgrade will cause the upgrade to fail.

l If multiple NEs need to be upgraded in the enterprise network solution, upgrade the NEs in the following sequence: the eOMC, the eAPP, the core network device, eNodeBs, and UEs. Unless otherwise specified, the eOMC910 can be upgraded independently without affecting services. The upgrade of eAPPs interrupts related services, and the upgrade of core network devices interrupts all services. eNodeBs can be upgraded in one or multiple batches based on the quantity of eNodeBs and related services are interrupted during the upgrade. UEs must be upgraded gradually after all the other NEs are upgraded. UEs that are not upgraded may not support new features in the target version.