how to alter audio levels

First, try the Amplify effect on each sample/clip. Audacity will pre-scan the selected audio and default to whatever gain is needed for 0dB normalized (maximized) peaks. So, just click ‘OK’ to normalize/maximize the clip.

They may not sound equally-loud with equal peaks, so if that doesn’t work, try the [u]ReplayGain plug-in[/u]. Again, you’ll need to apply ReplayGain to each sample/clip separately.