Extend Partition size.

If you are unable to extend a partition due to the option being greyed out, start by opening CMD.Then type diskpart, you will then type list disk this will list all disks, then type select disk # (Replace# with number), you will then type select part # the number locking the partition is usually 4 or 5, lastly type delete part override this will remove the partition blocking the extend.

You should then be able to go back to the partition screen and extend.