I3-3217U with HD4000 and no dedicated GPU?
10~40fps seems to be exactly what you should expect.
On my i5 3230m HD4000, I get between 20~30 with a 30fps cap. Okay at a hotel for a game or two... but I'd lose my mind if it was my gaming machine and not my work machine.
High Performance should give better results than Optimal (assuming you mean from Intel's driver software).
Run it at a reduced resolution, everything on low, make sure all other programs are closed you don't need.
Uninstalling won't make a different but you certainly won't have to buy the game.
If you have a dedicated GPU in there it sounds like it isn't using it or it's roughly equal to that of the HD4000.
There is an update coming soon.
http://answers.ea.com/t5/PvZ-Garden-Warfare-PC/Important-Messages-from-Twitter-PC/m-p/3155764#U3155764
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Here's a file to play with...
Open Notepad.
Copy and Paste this:
RenderDevice.ForceRenderAheadLimit 1
PerfOverlay.DrawGraph 0
PerfOverlay.DrawFps 1
PostProcess.DofMethod 0
PostProcess.BlurMethod 0
PostProcess.DynamicAOEnable 0
PostProcess.DynamicAOMethod 0
Render.VSyncFlashTestEnable 0
WorldRender.TransparencyShadowmapsEnable 0
WorldRender.MotionBlurEnable 0
WorldRender.MotionForceOn 0
WorldRender.SpotLightShadowmapEnable 0
WorldRender.SpotlightShadowmapResolution 256
WorldRender.LightTileCsPathEnable 0
RenderDevice.Dx11Enable 0
RenderDevice.Dx11Dot1Enable 0
RenderDevice.Dx11Dot1RuntimeEnable 0
RenderDevice.VSyncEnable 0
RenderDevice.TripleBufferingEnable 0
GameTime.MaxVariableFps 30
Save it as "user.cfg"
You cannot have user.cfg.txt
enable "View Extentions of Known File Types" from Folder Options in Control Panel
Put it in your PvZ directory
\\Origin Games\Plants vs Zombies Garden Warfare