My iPhone is not updated for latest version

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.5

• If you have an iPhone 6S through 13, you can update to 15.6.1

Go to Settings > General > Software Update.

Update your iPhone, iPad, or iPod touch using WiFi -

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

Update using your computer -

Update iOS on iPhone - Apple Support

I’ve Iphone 6plus and updated to 12.5.5. So what do I do now to update?

Your phone cannot update past iOS 12.5.5.

chejika wrote:

I’ve Iphone 6plus and updated to 12.5.5. So what do I do now to update?

You don’t. That’s as far as that phone can go. No further updates are available for the 6 or 6 plus.