Opening your system may not void your warranty, it depends on the builder. You should check with Acer or read the user's guide for more information. Usually, devices that are attached via PCI/PCI Express are more reliable, but there is no such thing as total reliability. A wireless extender should be used if you have flaky wireless where you use the PC, otherwise, it may just be best to use a wireless NIC. Have you considered using powerline networking
? The speed, depending on the configuration of your home or apartment, is about 200 Mbps. If the room with the router and the room with the PC are on different circuits, speed is reduced, but they are usually very reliable if you live in a house/apartment that can use them. They work by connecting your network to a wall outlet via a router or a powerline NIC connected to a router. You then plug a powerline network adapter into a wall socket near your PC. After that, you run an ethernet cable from the powerline NIC to the PC.