If you only want to convert your 8bit or 16bit displacement textures to 32bit and you think that doing that will somehow increase their quality, then don't bother, it won't. You can't add more information to map just by increasing its bit depth. You could do like dubcat suggested, displace geometry by low bith depth texture, tweak/fix/resculpt mesh and then properly bake displacement map from that geometry to 32bit texture, but the amount of work required for such operation, means that it's feasible only for single cases, unless you could find a way how to automate this process.