I have an IPad mini and I changed the Apple ID and the password almost one year ago and, for a while, a message asking me to sign in to iCloud pops- up constantly. My iCloud account is registered with an old email and password. I do not remember the

You will have to try to recover the password or contact Apple for help.

https://iforgot.apple.com/

Welcome to the Apple community.

If you are unable to remember your password, security questions, don’t have access to your rescue address or are unable to reset your password for whatever reason, your only option is to contact Apple ID Support, upon speaking to an operator you should explain that your problem is related to your Apple ID, this way you will not be charged for assistance, even if you don’t have an AppleCare plan.

The operator will take you through some steps you may have already tried, however they need to be sure they have exhausted all usual approaches before trying to reset your account, so you should try to be helpful and show patience with the procedure.

The operator will need to verify they are speaking to the account holder and may ask you some questions that only the account holder could know, and you will need to answer them if the process is to proceed.

Once the operator has verified your identity they will send a message through to your device which contains an alpha numeric code, which you will need to read back to them.

Once this has been completed they will send an email to your iCloud email address after a period of 24 hours, so you should check that mail is enabled in your devices iCloud settings.

Upon receipt of the email, use the reset link provided to reset your password, after which you should be able to make the adjustments to iCloud that you wish to do.