How to upgrade the firmware(4.05 CSV )on RT82?

How to upgrade the firmware(4.05 CSV )on Retevis RT82? Now Retevis RT82 have the last firmware version is 4.05, and it have 4 editions: Retevis RT82(CSV)-V4.05 Retevis RT82(CSV-GPS)-P4.05 Retevis RT82(GPS-REC)-S4.05 Retevis RT82(REC)-D4.05 It is well known that Retevis RT82 have tow models:GPS & NON-GPS, so we have  corresponding version for that. Do you know the…