Choose a file that either matches the size of your SD card, or is smaller than it. Use dd to write to the SD card.
dd if=/path/to/img-file.img of=/dev/mmcblk0
The card manufacturers keep on changing the capacity of the cards that we buy. So far ww've had to shrink the size of th card image 2 or 3 times. The (decompressed) image size is implied in the file name.