Why need passcode for software update ipad2?and how can we fix it?

Go into settings and turn passcode off and you wont have to

Because you are buying your app from the Apple App Store - some are free but some have a charge - there is no way round it. You need to have an apple ID and password for this.

It does not require a passcode, but you will need to enter your Apple ID password. All application downloads and updates require an Apple ID. You would have created one when you first setup the iPad. If you dont remember it, you can have it reset.

If its asking for an apple ID or iTunes account password then you need to sign in with that. If you forgot it you can recover it using the email account you signed up with. If you have a lock code on the tabket then it may be that one. You can sometimes sign out of itunes and sign in with a new one as well. This is a security feature to prevent apps from auto updating and wiping out settings or other people screw with it.