Transferring is not an easy process but it's definately possible. It depends a lot on your relationship with your PD.
If the PD is okay with it, and you have a good reason, it will be a lot smoother and you are unlikely to burn bridges. If the PD is not okay with it, if you do it just to get into a better program, or if transferring means you will leave the program short on manpower, then you may end up making enemies no matter how nice you try to be.
Transferring simply involves finishing a year (or getting your current program director to release you from the contract) and getting another PD to hire you. Most PDs who accept transfers want the former PD to write a letter saying it's okay for you to go before they'll even look at your application. So, you have to tell your old PD first. This prevents people from looking for new residencies behind the old PD's back - protecting the old boy's network.
Some PDs are known to be quite vicious if you try to leave, and either try to prevent you from leaving or fire you. They do this to scare others into staying. It's very unethical but commonly practiced.
If I were you and you were considering transferring, I'd ask through the grapevine what happened to the last person that transferred out. (and only ask people you really trust, otherwise the rumor will get out you're trying to bail). Unless you have a really good relationship with your PD, don't tell them you're leaving until you absolutely have to. Try to get a spot before you tell your PD, but give them enough warning so they can find someone to fill your shoes and not be short a resident.
