I have a Lenovo H520e with 4gb and a intel i3. I am not sure on the graphic card but I'm sure it's pretty bad. I can upgrade the i3 to a i7 920 but I'm not sure weather that's what I need to upgrade and whether I can. I would love some advise please as I am going to slowly upgrade my pc. 

First up, I would get hold of this little utility:

http://www.cpuid.com/softwares/cpu-z.html

It will analyse your PC and tell you exactly what the components are in the thing, which is important as you need to know what CPUs, RAM, GPUs etc your motherboard will support, so you need to know the exact motherboard, bus speeds etc, and it will tell you all that stuff.

My specs are

intel core i3 3240t                       

4GB memory

Intel(R) HD Graphics

 

 

They are extremely weak component's and appears you are using the on board graphics card 

I'm surprised you can actually fire up the sim with the default card 

The following benchmarks of your current CPU vs the i7 920 might be of interest - http://cpuboss.com/cpus/Intel-Core-i7-920-vs-Intel-Core-i3-3240T

 

Hey I am looking on buying a new pc. What would be quicker for p3d a amd a8-7650k or an i3-4160

I would recommend Intel CPU over AMD and not to rely on the onboard graphics card.  As for GPU stay away from AMD and go for nVidia instead.

If you want a good idea as to what type of PC to build/buy head over to Jetline systems and see what they have to run Prepar3D.