Login into your router and check wifi settings where you can see the band frequencies and take a screenshoot and post it here.
I got same troubles long time ago until understand that the settings for the wifi card depend of router settings, and others small factors like if in your aera there is a lot of routers from neighbours, walls, floors etc. (Explain a bit about your case)
Will try to help. Will change my windows language to english.
Are you on Windows 8.1 or 10 ? Is the signal from your wifi always strong wherever you are with the laptop ?
You should install those drivers : https://downloadcenter.intel.com/download/28621/Intel-PROSet-Wireless-Software-and-Drivers-for-Intel...