The furthest the iPad 2 can be updated to is iOS 9.3.5. If you bought your iPad in the seveal months it is probably already there. You can check your iOS version by going to Settngs > General > About.
If you've had the iPad long enough that it has a much earlier version of iOS, one that does not support Over The Air (OTA) updates, , then it may be necessary to use iTunes on a computer to update your iPad.
In either case, you can not update to versions before or after iOS 9.3.5.