Depends on where you're coming from, going to, how well you did at the institution you're leaving, and why you're leaving. You need to talk directly to the programs you're interested in. You pretty much have to go through the application process again. They may ask you to start at the beginning or they may let you start closer to wear you left off (but not likely exactly where you left off). They may not make you start at year one, but they may make you take some classes with the first years that you did not get at your last institution before you left.