How can I easily change the bitrate of MP3 files for free?

I have about 150 MP3 files that are 256 kbps. I want to fit all of them on a CD, so I need to change them to 128 kbps. However, every converter I've downloaded has limits, such as only a few at a time or only part of the file. ITunes makes a bunch of duplicates that are hard to sort out from the original. It's not a big thing I want to do. I just need to reduce the size of all these files. How do I do that easily and for free?

Why are you willing ---
nay, Determined ---
to accept such a downgrade in quality?

256 is bad enough!

I make CDs at the Best possible quality using WAV lossless and linear PCM.
Only when the material is MP3 to begin with (such as from iTunes)
do I accept lower quality, and then I Still make an audio CD from it.

I would use iTunes. Yes it makes duplicates but that's more for an in-case should something go wrong.

There's a section to find the duplicates in case you aren't aware
File > Library > Show Duplicate Items

I personally recommend 160kbps though. 128 is a bit too low imo.

CD's are less than $.25
use two.

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