Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
First I'd suggest to reset the password ***** your Apple ID. You can reset it from here --> https://iforgot.apple.com/
Go to the above website. Use the "Email Authentication" method to reset the password ***** Apple ID. Apple will send the reset instructions to the recovery email you setup with your Apple ID.
If that didn't work, then reset again and this time use the "Answer Security Questions" and answer the security questions there to reset your account password. After resetting the password, you will be able to use it with your iPad or iPhone.
Or you can contact iTunes Support to reset the password. To contact iTunes Support, goto this link --> https://www.apple.com/support/itunes/contact/
Click Contact Support at the bottom, click Contact iTunes Store Support at right.
Click Account Management. Click Lost or Forgotten Password
Click Schedule a Call and they will call you Or you can call them from there. Then you will have to answer some security questions and they will reset the password ***** your old ID. Then use it with iPhone or iPad
If you want to use the new ID instead, then you have to sign out old Apple ID from your iPad/iPhone. On iPad or iPhone, Go to Settings > iTunes & App Store. You will find your Apple ID signed in there. Tap it and tap Sign Out.
Then sign in to your new Apple ID. Remember, to update the applications downloaded using previous Apple ID you need the previous ID and its password. So if you don't have it, you have to delete those applications and redownload them from App Store using the new ID.
Tap and hold down the apps purchased/downloaded using old ID and they will start wiggling. Tap the x icon on them to delete them. Then go to App Store and redownload them using new ID.
To sign out from iCloud ID (if you have Find My iPhone or iPad enable), you need the password ***** old ID. If you don't remember or unable to reset it, you have to contact iTunes support directly to get it.
If you have any questions or would like any additional information, please don't hesitate to ask.
Remember, this is not my final answer. If my solutions didn't work please don't rate me bad or poor. Instead please reply back to me and I will continue to help you until we fix the problem or you are satisfied.