Which medical school are you currently attending? Which medical school are you interested in applying to? Why do you want to change schools? Many medical schools frown upon students leaving a LCME accredited school. If you have a legitimate reason to go to the new medical school (ie. spouse and kids established in a different part of the country, or dependent family members, like ailing parents), then you can probably try to transfer rather than doing AMCAS all over again. If you're insistant on doing first year over again, then I imagine that it'll be very difficult because many schools will be worried that you will leave them just as you left your current school. If you absolutely hate your current medical school and give that as your reason, then that's a poor reason too because what if you end up hating the new medical school? Again, they won't look favorably upon that reason.
I attended St George's in Grenada for two and a half years, and tried to transfer to a US school every year that I was there. I really want to pursue a surgical specialty and that was my reason to leave St Georges' since they have a poor track record of getting matches into competitive residency programs in the surgical subspecialties (like neurosurgery). So I redid AMCAS and got in to a US school with a history of producing matches into neurosurgery as well as general surgery. When asked why I am willing to "do it all over again", I tell them about my passion for surgery and that pretty much convinces them.