To download RSLogix 500 Version 8.1 (or newer versions that support the same hardware), you should use official Rockwell Automation
Important Notes
Since Version 8.1 is a legacy release, it is typically accessed through the following steps on the Rockwell website: Rslogix 500 Version 8.1 Download
As an alternative, you can try the following direct download links: To download RSLogix 500 Version 8
Minimum Software Versions Required to use the MicroLogix 1400 Operating System : Windows XP, Windows Vista, Windows