The issue is whether you're subject to the two year rule. If so, you must leave the U.S. and reenter as a tourist; if not you can attempt to change your status (with a timely application) without leaving the U.S.

A tourist visa is a nonimmigrant visa, so you can obtain one even if you're subject to the two year rule.

You can stay for the duration of your approved visit. Ask for the duration you need.