In order to file for a visa extension, your visa must not have already expired. Further, any violation of the conditions or terms of your visa, such as unauthorized employment, or criminal convictions while in the U.S., will prevent you from obtaining an extension.
If your circumstances have changed, there are additional possibilities. It is possible to change from a student visa to an employment visa, and also, if you are marrying a permanent resident or u.s. citizen, it is possible to adjust your status and obtain a green card.
Even after your visa expires, there may be methods of securing you legal status once again, but without question, it will more time consuming and expensive. Also, if you overstay your visa, and then leave the country, you may face a three year or ten bar on returning to the United States