Increasing the amount of ram will have no affect on the CPU speed. It will only be beneficial if you need more ram.That CPU does not have turbo boost technology and 1.9Ghz is the correct base speed.
edit: Did not see that it had speed step, I would also see if you can enable it, or if it is enabled like Y0GI pointed out.
I would try setting your power plan to higher performance mode and see if that makes a difference.