I have an iPhone 4 with iOS 71. I can't install apps from app store because when tap on install button of any app then showing error message " you most be update your iso device 8.0 or later version and try again..."
What can I do to install Facebook etc.?
I've been burned by this a couple times. On the app store if you look carefully it will give you system requirements. Lots of apps have a minimum iOS level.
So if you want an app that needs iOS 8 you need to upgrade your phone.
For most of this we need to want an app really badly to fork out that kind of money. Look for other apps with similar functionality.
Unfortunately the iTunes app store doesn't give you a filter to weed out the ones that won't work. Google is your friend here. Try
iphone app "iOS 7" | "iOS 6" followed by the keywords for the type of functionality.
