I would like to upgrade the processor, WiFi Card, and Graphics Card if I can in my Latitude E6520.
Current configurations (up to date if you check S/T):
The processor is removeable, so that can be upgraded - you'll need a Sandy Bridge generation CPU (not the later Ivy Bridge or Haswell). The wireless card is your choice - you can use anything that will fit in the system and take the standard antenna connections (probably two).
The video chip cannot be upgraded, nor can you add a video card. If you wish to upgrade the video, the mainboard must be replaced with one that has a discrete video chip.
If you do this upgrade, you will also need a new heatsink assembly.
Just to be clear I can install these items: