No, there is nothing to unlock. That is just the amount of available memory for userspace. You won't find an Android device that would report the total amount of RAM (it's usually ~400MB for 512MB devices, ~800MB for 1GB, ~1,8GB for 2GB, etc). There's quite a good collection of 'About phone' screenshots from different devices in CyanogenMod G+ page.
Blade III has 512MB of RAM but some of it used by GPU, radios, kernel ramdisk, etc. It is possible take back few MBs of RAM by changing certain kernel memory allocations though.