How/when are you trying to remove it ? You won't be able to do so when trying to download something, you will only be able to replace it. To see if you can remove it you need to just log into the account : Change or remove your Apple ID payment information in the iTunes Store - Apple Support
If you don't get the 'none' option on the payment details screen : Why can’t I select None when I edit my Apple ID payment information? - Apple Support