Samsung Galaxy S3 Toolkit Auto Update V7.3.2
Typically I prefer to do it manually. My Nexus 7 and Motorola Xoom both come with unlocked bootloaders from the factory (meaning I just issues the handy old fastboot oem unlock in fastboot mode). However, in an effort to save time this toolkit is pretty awesome. I have been using it since I got my Galaxy Nexus and it makes the process convenient.
Either method will work epicly!