[CentOS] change /etc/security/limits.conf need reboot or not?

We have CEntos 5.5 on DELL server.  Due to more and more databases run on same server sometime processes number read max and cause 'resource temporary unavailable".

I plan to change /etc/security/limits.conf value:

oracle          soft    nproc          2047 ==> 4096

Do i need reboot to make it effect?

How to test change is effect?

Thanks.