Welcome to JavaRanch. You can find a lot of useful information about the
SCJP exams in the
SCJP FAQ.
The difference between SCJP 5 and SCJP 6 is quite small. The FAQ has some information about what the differences are.
In my opinion, if you are already SCJP 5 certified, it is not worth the time, effort and money to upgrade to SCJP 6.