1. Open DirectX Diagnostic tools by typing DXDIAG on your search box select the result on the top of the search result as shown in the picture below.
This is how you open DirectX Diagnostic tools in Windows 10. If you are using other version of windows just hit CTRL + R button to open run and type in DXDIAG. There are bunch of tutorial on how to open dxdiag so I won't explain it here in details.
2. Press OK if a windows pop-up.
3. Now look at the system model, that is you actual model number.
1. Look at the back of your laptop, normally every laptop or PC will have a small sticker which shows your laptop model number. The picture below shows a sticker of a Acer laptop.
2. If there are a lot of number on the sticker, just use the serial number (S/N). Go to the laptop manufacturer support website and enter your Serial number. It will tell you your model and provide every support available for your model. Here is an example if you are using acer support site: