I would suggest reading the articles below as a starting point. If you don't need it for gaming the video card can be down-graded in some of the builds that are gaming focused.
If your power supply can handle the modern hardware then there's no reason to upgrade but I would at least consider it. You can get a new, good quality PSU for around $70. If you're not planning on overclocking the CPU, the stock heatsinks can be pretty quiet but if you want real quiet get a quality aftermarket model that's focused on being quiet.
