There are a couple good reasons why you might need to format your SD card. Perhaps you have tried one of the many available distributions on your Pi, such as Raspbian or RaspBMC, and are looking to make a change. Maybe you’re still running Noobs and are ready to step out and try one of the other operating systems we’ve talked about. Here’s how to perform an SD card format using either a Windows or Mac computer.
Now that you’ve chosen and downloaded the operating system, you need to prepare the flash card. The tool you’re looking for is SDFormatter. You can download the current version (4.0) here:https://www.sdcard.org/downloads/
Insert your SD card into the computer and make a note of the drive letter, e.g. F:/
Run the SDFormatter software. The screen you’ll see when running the software looks like this:
Select the drive letter for your SD card. Be absolutely sure you select the right one!
Click <Format> button
That’s it! Your SD card is now formatted and ready to use.