My wife lost her passport with valid visa, she is in legal F2 status,Can she still change her status from F2 to F1,without having her visa stamp?

In order for your wife to change status from F-2 to F-1, she needs a valid passport. Assuming that she gets a new one, she is allowed to change her status as long as she proves that she is still in legal F-2 status at the time of the request. If your wife does not have an I-94 entry/exit card, she can go online to the CBP (Customs and Border Protection) website to print out her entry information, and submit that along with other documentation including her dependent I-20 form. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.