FLAC codec is designed for high-qualitative music files. And its converter software should provide accurate processing. Read how to convert FLAC to/from other format, sound quality matters, etc.
Here you can find user guides for different kinds of FLAC file conversions.
What FLAC converter is the best for you, it's individual question. You can look for either freeware, or sound quality, or both, or others.
Here you can read more...