Latitude E6420 Windows 7.

Today I found my laptop was getting very slow internet. I checked and rebooted the ONT, router and laptop with no improvement. All my other computers and devices and those of other household members had not lost speed, just my laptop.

Typically at 5 GHz Wifi  the Laptop in my room gets
Ping 2 ms
Download 113.1 Mbps
Upload 19.3 Mbps

I now get

Ping 140 ms
Download 1.4 Mbps
Upload 15.6 Mbps

This leads me to believe the Wifi antenna in the laptop  isn't working properly.

How can I diagnose this and fix it?