How can I turn off where every time I turn on iPad or mail it ask for password

I Have the iPad 4, after last update I changed my Apple ID and password, but iCloud won't change the ID but it allowed the pw change so every time I turn on iPad or go to mail it wants the password. This is frustrating as I'm the only one on here. Help how do I save PW so it's not always asking for it Thanks Susiecue