The Tempo Editor lets you change the pre-programmed tempos of each song. To edit specific song tempos, be sure the song in question is selected in the left ‘Current Song’ field before entering the Tempo module.
When you initially click on the Tempo Editor button to edit a song, a dialog window “The requested tempo map was not found. Would you like to create a new one?” may appear. Click “OK” to proceed.

In the window that comes up, you will see columns for Measure, Beat, Tick, Division, and Tempo. To edit a value in one of the columns, double click on that field (or single click on the field to select it and click on the “Edit” button.)
 
To delete a tempo event, click on that event (in any of the columns) and click the “Delete” button. (Note that you cannot delete the first tempo event at the beginning of the song.)