This post explains how you can go about upgrading Raspberry Pi SD card size. You are likely to use this if you have already got your raspberry pi working but need more storage or a faster SD card. The guide is aimed at windows users but has instructions for Linux and mac users.
Step 1 – Copy existing SD image.
The first step involves copying the existing SD card image to the new (larger/faster) SD card. If you are using Windows OS you can use Win32 Disk Imager. If you are using max or Linux you can use dd. Instructions for this can be found on the following page.
Insert the SD card into your computer and once you have downloaded Win32 Disk Imager open up the user interface. First look at the device. Make sure you have selected the correct drive. Use windows explorer to check you have the correct drive (WARNING you can overwrite drives with this tool so make sure you check). Type in a file path (You cannot use the browse button as that can only be used for writing to the memory card and not reading) and then read to read the existing SD card image which will take about 5/10 minutes.
Once this has complete, put your new SD card into your computer. Now using Win32 Disk Imager and the file you just wrote, select the correct device drive (Make sure you check using windows explorer) and click Write. This will take another 5/10 minutes.
Step 2 – Upgrade the image size.
Put the SD card back into your Raspberry Pi. Your Raspberry Pi will not recognize the additional available space straight away (you can use df to check). To update the size run the raspi-config configuration tool.
Once this is open select the expand file-system option. Once this completes you will be asked if you want to reboot, select yes as you need to reboot for the changes to take effect.
Once your Raspberry Pi has restarted you will be able to use the additional space on the new SD card.