WiFi Speed maxes out at 20Mbps. Replace WiFi Antenna or Wireless Card?

[WhyStevenY]

I have a fast internet connection through Xfinity. Other devices can get up to 200Mbps. My HP laptop maxes out at about 20Mbps over WiFi. If I connect it via ethernet cable I can get 150-175Mpbs. I'm trying to figure out if I should replace my WiFi card (seems fairly easy). But, I'm wondering if it might be the antenna (which seems a lot harder to replace). Is there a way to know where the problem is?

Thank you for your help. 

[banhien]

@WhyStevenY 

The specs of your machine is

         https://support.hp.com/au-en/document/c04753170

It only has  1x1 802.11b/g/n WLAN  and  10/100BASE-T Ethernet LAN (RJ-45 connector)

You MAY BE ABLE to replace wifi card using

           ● Intel Dual Band Wireless-AC 3165 802.11 ac 1x1 WiFi + BT 4.0 Combo Adapter

or           Intel dual band 726x adapter

but to replace NIC card, you need new motherboard (or more soldering stuff). I'm actually using the following adapter for one of my old machines

              https://www.scorptec.com.au/product/Networking/Adapters/67965-USB-AC53-NANO

You can buy much cheaper elsewhere.

Regards.