Reset the memory in sqlserver 2008 and sqlserver 20082?.Do i need to restart sqlservices?.

I have to decrease the Sql server memory from 16gb to 12gb in sqlserver 2008 and sqlserver 2008 R2?.After changes do i need to restart sqlservices?.

As of my knowledge.If we increase or decrase sqlserver memory,No need to restart sqlservices from sqlserver 2005.Am i correct?

Thanks,

Ron.