You can also do most of this directly from your iPad.
'Settings', 'Store', 'View Apple ID'
There you'll have to enter the password, which I assume you know and then you could change the credit card details etc to whatever you want. You'll still have the same account, though - but you could charge it to your credit card rather than, say, your son's.
Alternatively, if you set up a new iTunes account, you can
'Settings', 'Store', 'Sign Out' and then sign in again with the new account details..
Tim
Scotland