Sorry, the nameserver ip 64.191.95.xx cannot be removing since it is till registered with a ICANN register.

how can i delete it from WHM so I can assign it to a new ns?

It has to be removed from all domains that point to your sever at whatever register you used or your customers used.

There's another thread about that here.
http://www.webhostingtalk.com/showthread.php?s=&threadid=119843&highlight=get+nameserver+IPs+back