"Extend Volume" function only works with contiguous unallocated space Next to the partition you would like to extend (on the right side). use 3rd party application.
I use gparted live cd, is open source and is faster than easeus partition master gparted.sourceforge.net
Faster didn't mean better! EaseUS is a well established Company which providing very good tools. I use the Server Edition since years without an single problem which I could not say about gparted! And the engine of the free version of EaseUS is the same as the one for the Pro and Server, just some limited features, which not need for home use!