COS for H1b to H4 visa transfer?

Hi, I got my H1b Visa approved last year Oct 2012, and started working, but now i am out of project and want to file COS from H1b to H4, How can i file my cos for H4 visa is already stamped, can i use same H4 visa stamping or do i need to file new H4 visa and again go for new stamping? 4) what if i go out of country and come back on H4, which is already stamped, as H1b is not yet stamped in my passport? Thanks for your help.

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