you can expand a volume only if your disk is dynamica, and also only if the disk was dynamic before you created those volumes in the first place. If you made the disk dynamic after the volumes were made, then you cannot extend the volumes. Also, you need free space available on the disk to expand the volume.
After you've checked all of that, go into disk management like anthony said, go to volumes, rt click on the volume you want to extend and choose extend volume... it's that simple.