To set options for App Store, go to Settings > iTunes & App Store. You can:
View or edit your account. Tap your Apple ID, then tap View Apple ID. To change your password, tap the Apple ID field.
Sign in using a different Apple ID. Tap your account name, then tap Sign Out. Then enter the other Apple ID.
Turn off automatic downloads. Tap Apps in Automatic Downloads. Apps update automatically over Wi-Fi, unless you turn off the option.