Q: MacBook Air Storage problem

I have recently checked my macbook air storage for several times.

Last night before I turned off my computer, it showed me that 14X GB of storage is used for 'other'.

And when I turn on my computer again today, it showed me that 218 GB of storage is used for 'other' now.

I have no idea how such large files can be stored in my laptop suddenly after one night.

Does anyone know how to tackle with this problem?

Also, I have just used my laptop for a year.

Throughout this year I have mainly used my laptop for watching youtube videos and going to social networking sites like Facebook.

I am pretty sure that I seldom download large files so I have no idea why I would have large 'other' files that contribute to over 140 GB of my storage at least.

I have recalled that there were several times of my computer turning off when downloading the apple software updates and that I may have downloaded same update files for repeated times. Does anyone know how I can check it from my laptop and clear it manually?

Thanks very much for your help!