How to Turn off wifi optimization?

[RossoneriFido]

Well I have S4 I9500 and whenever I tried to connect to my work network after updating to a clean android 4.3 OTA, I receive a notification stating that: This network has been disconnected.You need to sign-in again.
This also happened to all 4.3 users in my workplace. 2 colleagues using Note 3 and another colleague using S4 19500.
All of us can log onto various networks outside of our workplace like home and coffee shops...
After doing some research I found out that I have to turn off wifi optimization but that option is not available in S4.
Any suggestions?

 

[msndrstood]

I have a Note 3, not sure if it's the same for you but here's what I did. Settings >wifi >tap on menu key and choose advanced >turn off auto network switch. Hope this helps, worked great for me.

Sent via The Big, Bad, Beautiful Note 3

 

[RossoneriFido]

Yes I have already tried that to no avail on my S4. Didn't try it on Note 3 but will do.
Thanks anyways.