Install an audio editing program. This may include an advanced digital audio workstation like Reason, Sonar or Logic, or it may include a simple editor like Audacity, Amadeus or Power Sound Editor. You can download some of these programs for free.
Open your editing program. To open an audio file, click "File" on your menu bar and choose the "Import" option. Select an audio file using the navigation menu. In rare cases, your "Import" option may appear under a menu other than "File" menu.
Locate your "Tempo" or "Speed" option. In many programs, you will find a "Tempo" box right on your project window, usually indicated by the number 120 (120 BPM is a mid-tempo speed, and an industry standard default tempo for recording programs). If no "Tempo" box appears on your screen, check your menu bar options. Sometimes your speed option will appear under your "Effects" menu (as in Audacity, for example).
Enter a new number in your "Tempo" box. Higher numbers correspond to higher speeds, and lower numbers correspond to lower speeds. So 160 BPM would give you a fast, up-tempo beat, while 90 BPM would give you a slow, down-tempo beat.
Click the "Play" button on your software window to hear your changes. If you change the tempo too much, your sound quality becomes distorted, so use the effect sparingly. If you change the tempo too much, select (Edit > Undo) on your menu bar and try a smaller tempo adjustment.
Click (File > Save) on your menu bar to save your changes. To export your edited project as a self-contained song file (like an MP3), locate the "Export" option, usually under your file menu, and click it.