1) Right click “Notepad” and select “Run as administrator”
2) Click File -> Open 3) Browse to “C:\Windows\System32\Drivers\etc”
4) Change the file filter drop down box from “Text Documents (.txt)” to “All Files (.*)”
5) Select “hosts” and click “Open”
6) Make the needed changes and close Notepad. Save when prompted.
ETA: all credit goes to the users on reddit’s GW2 forum for posting this life-saving info!