You're going to need to adjust two things; the sample rate and the sample format. Hope you have a little patience for this because there's some mathmatics involved.
First, on your project, you'll want to adjust your sample format from 32 or 24-bit to 16, however when you change your sample rate, it'll change the speed of the audio. For example, if you're working with a 22.05KHz file, you'll want to adjust that down to let's say 8KHz (to reduce the file size); that'll be a 175% reduction in the sampling rate which you'll need to adjust back up. Experiment and adjust a little with the settings to find your optimal audio quality and file size settings. I'm still suggesting you use Audacity to do this where you can directly export your .WAV file from once you're done.