A web designer needs a computer with at least 16GB of RAM, a 27-inch monitor, and a quad-core processor like an Intel i7 to efficiently design websites. Upgrading components like the monitor, RAM, CPU, and motherboard would improve the computer's performance but cost between £50-2000 depending on the component. With adequate upgrades, the computer could remain functional for a web designer for around 3 years before needing to be replaced or further upgraded. Optional peripherals that could be useful for a web designer include a graphics tablet, printer, microphone, and webcam.