The only legally safe and technically reliable way to download is through the official GE Digital Support portal (often referred to as the "Support Site" or "Proficy Customer Center").
If you have an active maintenance contract:
If you are building a new SCADA system today, download iFIX 6.5 or 2023 instead. Use iFIX 5.8 only for maintaining legacy systems or if your plant’s hardware is locked to Windows 10 LTSB.