Quite a few owners have had this problem including myself, very frustrating especially for you as it is a recent purchase.
Appears the "restart" button does not always complete the update which throws up the "update failed" message.
If you are worried about causing some problems to your unit you could go back to the dealer you purchased it from and ask them to carry out the update for you.
Usually a manual switch off of the unit, wait a minute or so then switch back on and try the update again solves the problem.
Hope this helps.