To save the changes after you've deleted/changed anything with fdisk, choose 'w' to Write the changes to disk. It will probably tell you to reboot, but if you've not changed a disk that's actively being used at the moment you can most likely ignore that.
Once you've saved the changes, press 'q' to Quit.
Edit: Incidentally, typing 'm' will bring up a small menu with all the fdisk commands and their descriptions. That might help for future dealings with fdisk