Renewal of Visa (or more correctly your status) is done within the US to the best of my knowledge. You do not have to go out of the states unless you inisist. In case you get new document validating an adjutment of your status (whatever type it may be) then your status is current. Only in case you go out of the country, then you will need restamping of your passport. So technically once you are in the States, your visa is just a legal piece of paper with your photo id in it, and the little paper I-94 you get t the entry point is all that matter. The I-94 does not bear your photo ID, but actually now indicates how long you can stay in the US without violating the US immigration laws. It follows that the Visa i actually mainly for entry into the US territories. The temporary visa on my passport and the passport itsself had expired in my case, but before the I-94 cutoff date elapsed, I got my status renewed without my passport restamped, went home to Nepal, got my new passport restamped and came back to the US without a problem. No question asked! I hope my $0.02 helps, but do talk to your lawyer or friends! I do not see why you cannot visit Mexico and get your passport restamped there, if you insists this way.