Confidence is very different from arrogance.
Confidence means that you are aware of your power without needing to put yourself above others.
Arrogance = Bragging
Now, confidence is an inner attitude you can practice.
Start by taking a confident posture!
Stand or sit straight.
Imagine a string pulling you up from the top of your head.
90% of what the interviewers perceive from you is transmitted through your body language and your tone of voice.
A trembling or too low voice are absolute turn offs.
If you tend to be shy, practice speaking louder than normal.
Again it is something you easily get right if you practice it before an interview.