What if I don’t have wifi to update my iphone?

you will need to find a wifi network to use.. or update with a computer that is connected to the internet

Update your iPhone, iPad, or iPod touch - Apple Support

dessyerlangga wrote:

I am using cellular data now and I don’t have wifi to update my ios on my iphone 6S.

You just won't be able to update your phone until you have Wifi or you use a computer with iTunes to do the update.

Hello dessyerlangga ! To download any updates you need to connect your phone to WiFi connection. If you don’t have any WiFi connection, You can use any portable WiFi hotspot ( mobile data WiFi from other mobile phones) and update your phone. Hope these tips will help you.

Mcdonalds has free wifi. Anyone can use it. Don’t even have to go inside. Hope this helps.