Mother passed 2010 in Virginia. She has a safe box in Brockport,NY. I have copy of death certificate. What do I need to open and remove content of box

Unless the fee was paid all of these years, the box would have been long opened and the contents sold for the fee.  However, if the box is still sealed, and you should check with the bank, there is a proceeding to bring in NY Surrogate's court to open a box.  A death certificate is not enough alone to open the box.  You need a court order.