File Form I-539. See: http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=94d12c1a6855d010VgnVCM10000048f3d6a1RCRD
You can send out your application just about 10 days to 14 days before your OPT expires or earlier.
You can send out your application just about 10 days to 14 days before your OPT expires or earlier.