You can use Audacity (https://audacity.sourceforge.net/) where this is a setting to change the tempo without altering pitch.
You don't make yourself very clear, but if I understand correctly you're trying to modify the speed, but not the pitch, of a recording. In that case, you need a programme called 'Amazing Slow Downer' from Roni Music. (Google it.) Does exactly what you want to a high standard of fidelity. It's not free but it's quite cheap and worth it. Can't remember what kind of a demo version they offer.
Doh I missunderstood, disregard that.