On the HDD, the markings don't say "Master" and "Slave", but they do show how to set it to "Device0" or "Device1". I'd bet "Device0" is the first choice or "Master", and that's done by installing NO jumper.
I'm more intrigued, however, with the BIOS Setup screen that shows you have Master devices on both the Primary and Secondary IDE channels, but no slaves. I would presume this means that each device has its own cable connection to a mobo port. The HDD is connected as Master on the SECONDARY IDE port because that's where the cable is plugged into the mobo. Normally the system will try to boot from the Master on the PRIMARY IDE port. So I think you need to verify that both devices are set with jumpers to be Masters (they probably are already) and then switch the cables around between the two mobo ports. That would move the current Secondary Port Master (your HDD) to being the Primary Port Master, and likewise move the optical drive to the Secondary port as its Master.
By the way, why do you want to change? It is quite common on desktop systems to use the BIOS to set a boot sequence so that it tries the optical reader first and, if that fails, it goes on the the next choice, usually the HDD. Your BIOS may be set this way, and hence having the optical drive on the Primary Port as Master makes some sense. But you say you want to change this. If you do, make sure also to re-set the Boot Priority or Boot Order in your BIOS to correspond to your new hardware connection system.