Why isn't my Minecraft working efficiently?

So I have a Windows 8 Acer Laptop, Intel pentium 2.20 Ghz Processor, 64 bit operating system, 4GB of RAM, and i have all the proper plug ins such as 64 bit java. My minecraft runs extremely slow and I experience alot of lagg. But its only when I change my render distance or my difficulty off of easy. I can change my Graphics as fancy, clouds on, Smooth lighting at maximum and particles as all. I recently reset my computer to factory default and allI did was install the proper plugins for minecraft and minecraft itself. I figured out how to dedicate more ram to minecraft and I tried 2GB and 3GB and either way its never seems to change anything. I'm stuck at this point and don't know why its so horrible. Any advice would be nice. Please & Thank you.

Because its minecraft.

Have you tried using optifine? If not I would look into it. Its a mod you can download that can help boost fps. It gives you more advanced options for your graphic setting and whatnot

Factory Default causes more problems than it is worth. It loads All sorts of programs that you don't need and don't use. My first step would be to remove everything in terms of startup programs and start from there. Windows also runs "services", a vast majority of which you don't need. I would check them and stop, stop, stop a whole bunch of them.