My WhatsApp iOS is going to be outdated by 22october how can I update
How to update my iOS on iPhone 6
iPhone 6, iOS 11
WhatsApp is not going to stop working on your iPhone 6.
Your iPhone is capable of running iOS 12.5.6 so if you're updated to that, WhatsApp will continue to work.
WhatsApp is dropping support for iOS 11 and earlier.
If you do need to update your iOS -
Go to Settings > General > Software Update.
Update your iPhone, iPad, or iPod touch using WiFi -
Update your iPhone or iPad - Apple Support
Update using your computer -
Update iOS on iPhone - Apple Support