Open the device manager -- what shows under Display Adapters?  If you don't see two entries (one Intel, and one nVidia) you have only Intel video (which the vast majority of these will have).  The nVidia GPU was an option when the system was new -- one most buyers don't pay for.

Maybe try external programs like FurMark?

On the device manager it shows only intel. The 8gb are divided:

Total Available Graphic Memory: 8256mb

Dedicated video memory: 128mb

System video memory: 0mb

Shared system memory: 8128mb

I truly have it and thats shown at the 8gb. I don't think intel 5500 can be 8gb in size. Maybe I'm wrong. Afterall my laptop is working fine (it's relatively new). I've found drivers but they are only for win 7 or 8 and I have 10.

The RAM is shared system RAM.  The Intel specifications for that processor state that it can use up to 16G for video purposes (presumably that would require 32 G or more of system RAM).

It looks like your system does not have the nVidia GPU though - you can use the service tag at support.dell.com to look up the original specifications of the system.  However, if the system was purchased second-hand, it's entirely possible that someone, sometime replaced the system board.

CPU specs 

https://ark.intel.com/content/www/us/en/ark/products/85215/intel-core-i7-5600u-processor-4m-cache-up-to-3-20-ghz.html

It shows that I have it and it gives drivers too. The drivers are only for win 7/8. Maybe they changed it to use shared memory instead of gpu. I opened it and the gpu was there. Perhaps if I go back to win 7 I will be able to use it. Probably I won't anyway.

If the GPU is there, but doesn't show up in the device manager, check the system setup (F2 at powerup) to see if there' s a hardware setting to enable or disable the GPU.  This system is old enough it may have such a setting (newer ones don't;  they're controlled by software). I don't think this system has such a setting, but it's worth checking.

Bottom line:  the other possibility is that the nVidia GPU has failed (in which case the system will default to the integrated GPU).

I have searched in bios too it only shows intel. It may be smth about nvidia Optimus or whatever that was or I'm just not using it cuz I don't have the drivers. Anyway I consider this thread closed for me, thanks everyone!

Thanks!