Changing Bit Rate of Offline Content

[RapeKit]

Hello,

I initially filled my iPhone with music for offline play at 320 Kbits/s bitrate but eventualy found myself quickly running out of space due to other types of media on my phone and would like to now downgrade the files to 160 kbits/secs.

I have found where to do modify this on the Phone's music quality settings but nothing seems to change after puting it at 160 kbits/secs the files just don't seem to budge.

I have also tried clicking on & off individual lists via the Desktop Application under device: "iPhone 5" sync  as well as on the iOs App but nothing changes her neither.

Have I missed something on how to clear the content on my iPhone?

Regards,

Vincent