Access the manufacturer's web-site: http://www.acer.com
and select your model of ACER computer.
Select download-drivers.
Select the driver for your wireless adapter.
Download it.
Install it.
Select your OS and then download a wireless driver. Try it; see if it works. If not, download another one and try that. Repeat until you get the right one. I suspect it to be the Broadcom, though, but I'm not certain.