Virtual Server Memory not reflection post upgrade

We have upgrade Virtual Server memory from 4GB to 16GB through OFFLine mode only but the upgrade memory is not reflected in OS side.
Server running on RHEL 5.4 32bit OS.
[root@HKLVATQUC01 ~]# uname -r
2.6.18-164.el5
[root@HKLVATQUC01 ~]#