The latest version of Java - version 6 update 30 just became available today.
The red link in my signature will check what version you have installed.
The green link will provide instructions to remove the previous version and install the new version.
Except you will need to change the "29" to "30" as the site has not been updated yet.
Just performed the update myself and it's good to go.
If you have a 32 bit machine, the instructions are on the left down a ways, for 64 bit machines the right side has the instructions.
It says to remove the old version first and mentions the instructions for doing that are towards the bottom.
Then you just start from the top and copy and paste the commands and you should be good to go.
Myself, I used gedit to put the file name and change the 29 to 30. Then copy/paste as needed.
Then you may want to check out the How to in blue in my signature. It is really good for dual booting but, not just for dual booting.