What does 'not letting me download anything' mean, what happens ? If you are getting an error message what does it say ?
And for the removing of the card, how/when are you trying to do it ? You won't be able to remove it when trying to download something, you need to just log into the account: Change or remove your Apple ID payment information in the iTunes Store - Apple Support
If that is what you are doing and 'not allowing me to do so' means that you aren't getting the 'none' option : Why can’t I select None when I edit my Apple ID payment information? - Apple Support