Two scenarios, show me steps to get to both
I have two different scenarios
The first scenario is, I want to be able to have the latest ROM (Android Rev. to be exact) along with the latest firmware. How can I do so? Show me the steps involved, e.g. S-OFF first (is S-OFF even required to begin with?), root it, what to install, what not to install, etc.
Second scenario is, and this is different from the first. I want to return to 100% Stock, so that I can return my phone safely without being recharged a hefty fee. How would I do this? By 100% stock I mean stock ROM, no mods, stock firmware, stock everything, able to receive OTA updates from AT&T, no TAMPERED sign, no UNLOCKED sign, etc. Basically no signs of any modding or rooting whatsoever so there's no chance they'll charge me.
My CURRENT scenario is: AT&T Phone, currently on Android Rev. ROM, not sure which firmware version, UNLOCKED, S-ON.
What to do to achieve both scenarios?