1. Reboot the iPhone 5s. If this doesn't work go to step 2
2. Forget Wi-Fi Network
- Tap on setting on your device - Tap on Wi-Fi option
- Tap on the running Wi-Fi network
- Tap on "Forget This Network"
- Tap on "Forget"
- Then rejoin this network and re-enter the password. Then check if the issue has been solved
- If step 2 is not working try fix no.3 as below.
3. Reset Network Settings
- Tap on "Settings" --> Tap on "General"
- Find "Reset" and Tap on it then --> Reset Network Settings
- Then try if the WiFi is working
- If NOT working then try fix no.4 as below
4. OpenDNS or Google DNS - if the above solution is not working try to use this method. Manually set the DNS to public DNS.
- Tap on "Settings" again --> Tap WiFi option.
- Tap on the Wi-Fi network you are running you will see IP Address, Subnet Mask, Router, and DNS Tap on DNS and set the Primary DNS and Secondary DNS separated by comma like so: (22.214.171.124, 126.96.36.199).
- This will work if your network DNS keeps on changing by using the public manually set you are always on public DNS.
So hopefully you can fix your iPhone 5 WiFi problem with iOS9, Cheers!.