To fit a new sound card choose a PCI sound card you wish to fit, almost any will do.
1. Prepare, and earth yourself on radiator or use antistatic wriststrap.
2. Open PC up
3. Remove a spare slot cover for a PCI slot on the PC case.
4. Insert sound card firmly but carefully into the PCI slot, image: click here
5. Then ensure fully flush, and screw in.
6. Put PC case back on.
7. Then in the BIOS disable the on-board audio in the Peripherals area.
8. Then in windows, install the drivers for your new Card.