It does not matter what partition the AP is booted in. WiNG 5 devices allow unused partition for staging purposes and to reload at a later date. If you wish to boot into v5.7.0 (highly recommend v5.8.6.1 or v5.9.0), from the CLI, perform the followng:
enable [enter]
boot system xxxxx [enter] (xxxx represents primary or secondary partition)
reload [enter]
AP will boot into the partition you selected for next boot.
Again, it does not matter what version is in what partition. Only what partition you are booted in.