16GB memory card, ive used 2GB and yet have 14GB of free space, how can i use that 14GB and why is it saying low of space on sd card???
This may be expected, depending on what phone you are using.  The original standard of SD card readers had a 2GB limit on them.  These readers could read cards that had more space, but only had enough memory registers to read the first 2GB of them.  Sometimes a firmware update can increase this from 2GB to 4GB, but it's extremely rare.

From the wikipedia article on the SD standard:


Capacity
SDSC (SD): 1 MB to 2 GB,
   some 4 GB available.
SDHC: >2 GBs to 32 GB
SDXC: >32 GB to 2 TB,
   some 32 GB available.