When changing your Status, once you leave the U.S. you would no longer be able to enter the U.S. again in that status and you would have to start the process from the beginning overseas to get a new visa. If you have a current Multiple Entry Visa, it might be better to return to your country prior to your I-94 expiration date and come back into the U.S. rather than losing your current visa.
In extending your status in order to remain in the U.S. longer you will need a good reason that is acceptable to the government and have documents to prove it.
When attempting to change your status (as student, worker, etc.) or extend your status in order to stay in the U.S. longer, please keep in mind that if your current stay expires (date in your passport) the government could denies your request. If the government (USCIS) denies your request after your stay has expired you will be considered out of status (Illegally in the U.S.) from the expiration date listed in your passport. As a result, you will have very difficult time getting admitted to the U.S. or having a Visa approved in the future.
You should always try to request an extension or change of status at least 45 days prior to the expiration date in your passport. If you have made a request less than 45 days it may be better for you to leave the U.S. if you have not received an answer from USCIS prior to expiration date in your passport for your current stay.
Please contact a licensed Immigration attorney before you act on your specific situation. Immigration Laws and Federal Regulations are constantly changing and the general information provided can change over time.