Hi, I am thinking of buying certified pre-owned S5 from T-Mobile. It comes with 4.4.2. for some reason.
Is there any reason I cannot upgrade the OS when I receive it?
As long as it is a T-Mobile S5 you should be able to. Here is a list of the software updates for the T-Mobile variant. The 4.4.2 version should match the one on this list then you should be able to update it to the latest version shown on this list.
Software versions & updates: Samsung Galaxy S 5
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