If you want to be careful then do it same as seen from this video,
youtube:
https://www.youtube.com/watch?v=e_NpHQmmn28
Another way (as i do it) is to get your fingers under front I/O and use some muscle power to pull the front I/O off from the case. Here's another video where this method is demonstrated,
youtube:
https://www.youtube.com/watch?v=uY6dZmbURbc#t=0m25s
While 2nd method is faster, you can break the front I/O plastic if you pull too hard.
2nd method is for those who have more experience on what they are doing and aren't afraid breaking the front I/O.
1st method is good for beginners, while it may take longer, the end result will be the same.