This type of situation is quite common. Sometimes your upbringing, your culture and even your age may block out your ability to communicate even with your peers, let alone the management.
Stay assured that it will pass as you progress through your career and your life. If speaking to upper management is part of your job and is inevitable, ask your immediate manager to help your train your communication skills. If this isn't an option, look for communication courses yourself.
Remember that everyone at the company is a person just like you. Everyone is pulling in the same direction to do their jobs, achieve the goals and help the whole company succeed. If you need to talk to anyone, it's because you also want to help the company succeed. Remember that they want to listen to you as well, for the same reason. So don't be afraid, you are only doing your job.