Realtek manufacture many chipsets for computing hardware, most often for sound cards. Windows Update can normally provide recent drivers automatically for this type of device, however if you are experiencing sound problems it may be worth updating your driver to the latest release manually.
Visit the PC Audio section of the realtek website at the following link, and then select your sound card from the navigation menu:
If you know your product code (for example "ALC850") then you can type this in to the search box for instant access to the product driver page.
If you have an onboard sound card it may be worth checking with your motherboard manufacturer website to see if they have the appropriate download already.