The most secure method is through the Siemens Industry Online Support (SIOS) portal. You will need a registered account and, in some cases, an export-controlled clearance.
The 4.91 update remains a stable industry standard for legacy systems and specific SIPROTEC 4 hardware versions. siemens digsi 491 download exclusive
If logic won't compile, verify that the correct device driver (Device Catalog) is installed for your specific relay firmware. The most secure method is through the Siemens
Help you between your PC and the SIPROTEC device. in some cases
Smartphones 
Mobile SoCs
Graphics cards
Games
Processors