Increase RAMDISK_SIZE on CentOS 64

I like to increase the ramdisk_size=150000. How do I do that ?

Here is my Kernel cmdline

cat /proc/cmdline

root=/dev/xvda xencons=tty console=tty1 console=hvc0 nosep nodevfs ramdisksize=32768 ipconntrack.hashsize=8192 nf_conntrack.hashsize=8192 ro devtmpfs.mount=1

Thanks