This tutorial will help to install an internal Bluetooth v2.0 adapter into your Acer Extensa 5420 notebook. I think this tutorial might work for Extensa 5620 notebook series too, but I’m not 100% sure.

For this upgrade you’ll need a compatible 4-pin internal Bluetooth adapter, you can find it here. Make sure to contact the seller and confirm that you are getting a compatible adapter.

The Bluetooth connector is located on the motherboard under the touchpad and the author explains how to install the Bluetooth adapter without taking the whole thing apart.