General ics update - what will happen?

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http://androidforums.com – Hi guys, i have an arc s and have noticed the ice cream sandwich update is available. What i was wondering is, will i lose anything on my phone when i update it? The reason i ask is i had an x10 last year and when it had a new software update i updated the software and it wiped everything off my phone and i was gutted. So I'm a bit scared of doing this in case it happens again. So if anyone would be able to let me know i would really appreciate it. Thanks in advance for any help given :) (General)