This command should tell you what is currently providing the Java virtual machine (
java) and the Java compiler (
file /etc/alternatives/java /etc/alternatives/javac
This assumes the "alternatives" system is working properly, which might not be the case, depending on how Java has been "messed up" in the past. To check this, run:
file `which java javac`
If the alternatives system is working correctly and being used by Java, then you should see:
/usr/bin/java: symbolic link to `/etc/alternatives/java'
/usr/bin/javac: symbolic link to `/etc/alternatives/javac'
Otherwise please edit your question to provide details. Then it should be possible to give a more specific answer.
You can remove
openjdk-6 with the Software Center. There are multiple packages associated with it, so you may need to remove more than one packages. (All the `openjdk-6 packages are listed here.)
Or you can use the command-line:
sudo apt-get remove openjdk-6-\* icedtea-6-\*
However, whichever method you use, you may want to check first to see what depends on these packages--you might have software installed that specifically needs version 6. (Probably not, but possibly.)
You can check for this by simulating the removal operation on the command-line:
apt-get -s remove openjdk-6-\* icedtea-6-\*
This will show you the effects of removing those packages, including what other packages would be removed as well. (You'll notice that since this is a simulation, you don't need
openjdk-6- packages (except perhaps
openjdk-6-jdk), you should make sure you have
icedtea-7- packages installed corresponding to whatever
icedtea-6- packages are installed.