adding nr_uarts=20 kernel parameter - HOWTO?

I have two PCI-800H byterunner 8 port serial interfaces.
They work on my old RedHat 9.0 system.
I have upgraded to RHEL6.5 which seems to be just fine, but
I have not found out how to configure the ports to 20 so the
16 ports on the serial cards can work. (No ttyS? beyond 4.
I need 4-19.

Several references I have found recommend the nr_uarts kopt
in menu.lst in /boot/grub. There is no KOPT= line in my file.
Where do I go to move ahead?