Performance increase by switching from low sp to high SP and back to low SP

Hi Guys,
I’m sorry but I’m new to unreal engine and oculus, I’m trying a simple scene and experiencing stuttering problems when using oculus, so I’ ve tried to scale down antialiasing, shadows and post process, getting better performances but not enough to have a fluid vision.
now the question is what do you mean when you say " switching from low sp to high SP and back to low SP "?
What do I have to do to switch from high to low and back?
Any other good suggestion to increase FPS?
Is it true that under 75 Fps oculus DK2 will give stuttering problems?
Thanks to evereybody