Extend volume where unallocated space lies ahead of it
Solution 1:
Since Windows`s disk management surely could not extend the partition when the unallocated space is on the left of the partition, you have to use a third party partition software.
In the link below are described the steps of expanding unallocated Drive Space "From the left".
http://www.petenetlive.com/KB/Article/0000678.htm