*Note that clearing the cache and hard resetting are not necessary unless it doesn’t boot! Otherwise it’s a waste* Tutorial on how to Flash Jelly Bean to i9300 with ODIN. This method can be used to flash any appropriate rom! Just make sure it is the right one for your phone! Only use this link for the i9300!!!
Find the links to ODIN and XXDLIB Here!!!
(Example of what not to do lol – and how they fixed it) http://forum.xda-developers.com/showthread.php?t=1792765