Hello,
If this is a prduction server I would move to 6.01 ASAP. I know there are some security issues with 5.5.
When I upgraded to 6.01 from 5.5 Here is what I had to do. A search will reveal alot of this stuff too
-backup
-do an upgrade from 5.5 to 5.6
-double check everything works
-backup again
-upgrade to 6.01
-perform the webmail password bug fix (Check the bug tracker)
-check everything is working
-backup again
if you are then moving everything over to a new hard drive, and its over 2 gig's you will need to rsync everything over to the new server. A search will reveal the fix, I don't remember the link off hand.