Backup your files:
Simply plug in a USB thumb drive and copy your documents over.

Backup the entire RPi Image File
It's a good idea to back up the entire image file from time to time.

    1. Install your RPi SD card into the card reader on your PC and note the drive letter assigned.
    2. Run the Win32DiskImager program.
    3. Make sure the Device field contains the drive letter of your SD card.
    4. Type the path and filename you want to use into the Image File field OR use the file button and 'drill down' to the folder you want and type the filename. The filename you choose must have the .img extension. It's a good idea to include the date or some kind of sequence number as part of the filename, for example:
    5. Click on READ. Backup will take quite some time depending on the size of your SD card.
    6. The saved image can now used to restore your image to the SD card later or to another SD card.