Before update make sure you take your database backup and script backup from server so in case if anything goes wrong you can restore it.

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Before update make sure you read this FAQ.

• Q. Will This Update affect my existing data eg. product data, orders?
  Answer: No it will not affect your existing .


• Q. Will This Update affect my customization eg. in CSS,JS or in Core code ?
  Answer: Yes it will affect your changes if you did changes in code files
  If you customize CSS or JS using Admin -> Custom Style Setting Than all your change will not affect else it will affect.