How can an iOS update help me?

OvuRichard ~ What problems do you need help with? ...With an older model such as your iPhone 6, some problems can be due to the battery. So does your iPhone 6 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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Safari is updated when you update the iOS on your phone. Your phone cannot be updated beyond 12.5.7. It looks like it is already there.