How to switch off data roaming on iphone 4s?

I'm trying to avoid any additional charges when i go abroad but can't see how to switch off data roaming.
I have iphone 4s. I have looked on line and it says to go to general, then network but i don't have a net work button.
In general i have;
About, software update, siri, spotlight search, text size, accessiblity, usage, background app refresh,
auto lock, restrictions, date & time, keyboard, international, itunes Wi-Fi sync, VPN, reset.

I have been into all of them and can't see data roaming button.

Can anyone help please?

Settings > Cellular > Roaming > Data Roaming and Voice Roaming (on/off)

Just tell Siri "go to data roaming" and you will see it.

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