[CentOS] set lockedmem to higher value?

We have some ORACLE PGA problem and ORACLE document say we can serup lockmem(Max lock memory) to higher value.

$ulimit -a 

time(cpu-seconds) unlimited 
file(blocks) unlimited 
coredump(blocks) 0 
data(kbytes) unlimited 
stack(kbytes) 10240 
lockedmem(kbytes) 3145728 
memory(kbytes) unlimited 
nofiles(descriptors) 65536 
processes 2047 

Can anyone tell me how to set lockedmem to higher value on CENTOS 5.4?

Thanks.