Support questions about zte merit (not rooted) (Net10)

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http://androidforums.com – Ok, I bought this zte merit z990g from Net10 back in Feb (runs on at&t towers) I was sent a text yestetday telling me to follow the link to update my browser, yet when i did, nothing happened. Also, Im needing to know can I change the gingerbread stock to a different one, or will that mess my phone up? If so, how to I go about that? I know I need to download the update.zip but I have no clue as to how to do it or whats the best thing to use. This phone has NO memory space at all :-( Also, is there a way to restore my internet, because Net10 's unlimited plan is no longer unlimited (General)