New
#11
before you can extend, you need to move the partitions next to the one you want to extend like I is next to C
now you need to delete partition I in order to create the empty space, partition C can be extended into.
If there is no free room next to a partition the extend-option stays gray
Make sense?
OK if you still want to merge I and J, move J next to I, delete I and then extend J into the newly created empty space
-DG