Now i updated my phone using SEUS (Sony Ericsson Update Service).
It is successful.
PC companion does not give detailed instruction while SEUS tells you the instruction to update your phone. So, better get SEUS if you do not have it.
If you just only update your phone software without making changes with your internal data, then you might do so without doing any backups.
If you want to be safe, then go to android market to find some applications to do the backups process and save them into your computer. Check the posts above.
