Japanese people greet each other in many different ways depending on the time of day. Some greetings also differ depending on the relationship you have with the person you are greeting.
One can also say just "Ohayou （おはよう）". This is casual, and should not be used with one's boss.
Please check out the instinctual video, How to Say Good Morning in Japanese to learn the pronunciation of Ohayou gozaimasu.