Main documentation: The following 2 items explain the Inplace Upgrade process. No 1) shows the basic idea and No 2) goes even more into detail:
(Important: Please follow all the steps in No 2) exactly in the given order and plan enough time for tests)
2) http://www.microsoft.com/en-us/download/details.aspx?id=14599 (Note: This used to be updated about every 3-4 month, so it makes sense to check here for updates)
Best practice advices:
As an extra effort please share the following hints to your colleague Amit regarding AX object ID conflicts:
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