Last firmware is : DH_IPC-HX5XXX-Volt_MultiLang_PN_Stream3_V2.820.0000000.5.R.210705 ( 05 juillet 2021 )
but with your firmware you have manual focus , no need to upgrade.
no need to use 25 fps ! you can use 10 fps for LPR , 15 fps is good , only shutter speed will affect the result.
You can...