Change Speed
From Audacity Manual
Use the Change Speed effect to change the speed of a track, affecting its tempo, pitch and frequency content. When you slow a track down, all its frequencies become lower, and when you speed it up, they all become higher.
To change the tempo of a track without affecting its pitch or frequency range, use
or .The Percent Change input box, slider and Standard Vinyl RPM popup menus are all linked: changing one will change the others.
Percent Change
If you know how much you want to change the speed of the audio in percent, enter that value here. You can also drag the slider to choose a Percent Change - the input box will update as you drag the slider.
Standard Vinyl RPM
If you have a recording of a record that was played back at the wrong speed you can correct that using these two popup menus. In the from popup choose the speed the record was played back at; in the to popup choose the speed is should have been played back at.