Your OS version will be listed as a series of numbers after a lowercase V (v18.104.22.168) on the first screen.
You can also employ the Help Me screen shortcut to determine your current OS version by hitting ALT, SHIFT and the letter H.
If your carrier does not officially support OS 4.5 then this is useless. I haven't had a chance to check into exactly what version of OS4.5 it will spit back yet (and whether or not all devices/carriers are supported), so if you give it a go be sure to report back in the comments with your findings and experiences.
Our buds over at Berry Review have summed up the situation nicely so I'll borrow from them on this: Looks like the Web Upgrade for OS 4.5 we mentioned before is limited by your PIN # and its association with your carrier. Follow all of the instructions and you will soon have yourself the latest offical OS for your Black Berryd device.Before you begin, make sure you have the latest Black Berry Desktop Manager (DM) available at RIM’s site: Black Berry Desktop Software – Black Berry Software at Black Now that you have the latest DM we can continue with upgrading your Black Berry OS. Run the DM and select Backup/Restore, then Backup and select where you want the file saved.The Black Berry OS is a proprietary mobile operating system developed by Black Berry for use on the popular line of Black Berry Smartphones.If you've been itching to try out a new leaked OS, now is your chance. Don't get too excited clicking and hoping to update anything just yet.