You can directly upgrade to FUS 1.9, there is no need to upgrade 1.7 first. Note that the upgrade of the FUS can take 30-60 minutes! You should do that only while you have a connection to the console port, to ensure it's progressing correctly. If you plan to upgrade to 8.5.x, upgrade first to 8.3.x! And to upgrade to 8.3.x you should first upgrade to 8.2.x.
My suggestion is the following:
- FUS 1.9
- 7.4.150.0
- 8.0.152.0
- 8.3.141.0
- Optional 8.5.130.0 (should be out by tomorrow)
Very important, always leave enough time for all APs to upgrade to the new code. If I remember correctly, the 5508 WLC can upgrade 5 APs at the same time. Every upgrade of those 5 APs takes ~5 minutes without counting reboots. So with 30 APs, it will take you 6x 5 minutes -> 30 minutes, plus reboot of the WLC and the APs. That again means you will need around a full day for all the upgrades.
Unofficially you can probably upgrade directly from 7.4.x to 8.3.x, but that's probably unsupported by TAC and could cause configuration issues.
After that you can upgrade, 8.5.130.0 should be out today or tomorrow. I would either take that release or 8.2.166.0 (8.2.170.0 should also come out in the next 7-14 days, more likely 7) or 8.3.141.0.
