An excellent free audio sample rate converter.
Most old software converter doesn't have accurate algorithm so this will take care the down sampling part for you.
Voxengo r8brain - Free Sample Rate Converter Tool
Free Sample rate conversion application. Allows you to convert any PCM WAV audio file of any sample rate and bit-depth to another sample rate and bit-depth. Batch processing is available.
www.voxengo.com
Most old software converter doesn't have accurate algorithm so this will take care the down sampling part for you.