I have an iMac and I'm trying to upgrade to Mountain Lion but I encountered a problem, I'm about to install Mountain Lion but it says it cannot install because my HDD is not a Mac OS Extended (Journaled) format. I went to disk utility and checked my startup partition and it shows Mac OS Extended only. How can I change it to Mac OS Extended (Journaled)? I'm hoping to change it without deleting the contents of my HDD, I'm just really hoping to do an upgrade and not do a clean install. Any help or suggestions will be greatly appreciated. Please advise. Thank you.