[How to update drivers]
Open up Device manager, expand Network Devices, check the brand/model of both ethernet and wireless network cards. Go to the brand manufacturers' websites, download/install the latest drivers from their sites.
[using wireless]
Tried wired?
[Router = RT-N66u]
Tried updating the firmware?
Eh? How is it not possible? Run ethernet cable from PC directly to modem and see if you still have packet loss issues. If not, then issue lies with the router. If so, then it's either the modem or something with your PC.