Can I update iOS8 to iOS11?

pu1. I don't think there's any reason not to update it Even if it's for security reasons

2017-12-19

OK

pu2. It's better to do it for security

2017-12-19

OK

pu3. I think it's better to just use it because there's a problem that the phone slows down when I update OS. In the case of iPhones, there is a rumor that the iOS update slows down the phone every two years to buy a new phone

2017-12-19

OK