What do I need to Upgrade to play high end PC games?

Hello I was just woundering what I need to upgrade in my desktop to play better games with no lag such as Far Cry3 Skyrim minecraft with X512 texturepack and mods saints row 3 & 4 etc…

These are my specs in my computer right now

Processor: Intel(R) Core(TM)2 Quad Cpu Q6600 @2.40ghz
installed memory: 8.00 GB
System Type: 64-Bit operating system/Windows 7
Motherboard type: DDR2
Graphics Card: NVIDIA Quadro FX 1700

on a side note I meet the requirements for skyrim but still lag
on all low settings same with saints row 3

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