Solved! Can I upgrade Alienware 18 graphics card?

Solution
No.
Laptops generally have extremely limited upgrade options, typically you can upgrade the RAM and/or the HDD/SSD. The rest of the components tend to be soldered directly to the system board and can not be replaced.

Some Machines include a thunderbolt port which allows you to use an external GPU, however, Thunderbolt typically only delivers a total of 4 PCIe datalanes when most single GPU's benefit from 16. As such external GPU's are always severely constrained for bandwidth when using thunderbolt connections.
Thanks for the image, but that doesn't tell us anything about the current graphics card it has.

Typically, mobile GPUs cost a lot and are very difficult to replace. Like $400 for a used GTX980m that's going to perform less than a $200 desktop GPU and overheat inside the laptop.
 
No.
Laptops generally have extremely limited upgrade options, typically you can upgrade the RAM and/or the HDD/SSD. The rest of the components tend to be soldered directly to the system board and can not be replaced.

Some Machines include a thunderbolt port which allows you to use an external GPU, however, Thunderbolt typically only delivers a total of 4 PCIe datalanes when most single GPU's benefit from 16. As such external GPU's are always severely constrained for bandwidth when using thunderbolt connections.
 
Solution
The service tag is what you go by to see the system specifications (a normal procedure for Dell). You hid it in the picture. Without it there is no way to know for certain exactly what is in that laptop
 
it doesn't matter what's in it, you can't upgrade it. you upgrade a laptop in that case by buying another one, but as stated, even the most powerful laptop card is a poor performer next to even an average pc card, and they love to overheat.
 


You can use internal PCIe connector but you would need GPU riser with this type of connector and external power supply to power the GPU and the GPU itself.
 


I see, that would definitely be as you say, not really a laptop anymore... Wouldn't this type of config need an external display too?
 


The GPU will appear in device manager so you should be able to use your GPU with the Laptop display, after you install the drivers obviously.