I believe the Disk Management console will allow you to resize your C drive in your case. If so, you can right-click on the 116GB partition and it should be an option. Other people suggest using Partition Wizard, which is free. I can find you a tutorial for that. It wouldn't be a bad idea to have any important data on C backed up.
As for the drive letters, I always move my optical drive to be E using Disk Management. I prefer to have all of my hard drives in line, then optical drives, and then any external or network drives at the end of the alphabet. You can change drive letters other than C by right-clicking on it in Disk Management.