If I just accept paypal as payment (and not credit cards), how do I remove those credit card logos that appear on the PayPal button?
Depends on whether your site is hand coded and you added the PayPal button yourself (can be found on the PayPal website under tools), or whether it is a CMS site and it's a generic PayPal button.
That's the simple answer, because if it is hand coded and you added the button yourself from the PayPal website (after login in), then there is a multitude of choices of PayPal button to choose......
Otherwise on a CMS site you will have to use what is available..... perhaps with a polite notice that credit cards are not accepted.
It is possible to edit the PayPal button if hand coding... but I strongly advise against it, you will probably be breaking PayPal terms and who want's to click on a PayPal link that looks unusual? NOT ME!
But the main issue you are overlooking is that nearly all payments through PayPal are by credit card! The credit card payments do NOT refer to YOUR accepted payment methods..... but their (PayPals) accepted payment methods.
So the query really makes little sense............... as PayPal takes credit card payments on YOUR behalf and advertises which cards can be used for your customer.....