Can't modify partition options in v10.8.5

I am trying to update OS 10.8.5 to Mavericks and I'm getting the "this disk does not use the GUID partition scheme...". Since I already have OS 10.8.5 installed, I assumed the root partition was already using the GUID partition scheme. While the recommended course of action is modify the partition options within the Disk Utility>>Partitions tab, the 'options' button below the partition display is grayed out for all partitions including the OS partition. I confirmed that FileVault is NOT enabled for any partitions. So why is still grayed out? Or more importantly, how can I unlock these features or refresh the GUID status as far as it's seen by Mavericks installation? FYI, I repaired disk permissions without incident and the problem persists. What is also puzzling is that the Mavericks gives me the option to install on the second hard drive I have installed in my MacBook Pro. For starters, I'd like to be able to access partition options.

Any help would be much appreciated!