Clarinettists may have varying reasons to alter an audio file for their own use.  If you would like to practice a work at a slightly slower tempo, or if you need to change the pitch, these can be accomplished easily with free software.  

If the audio file is in the form of a CD, you will need to "rip" it to a computer (if your computer doesn't have a CD drive, try a local library's computer, or they are otherwise easily purchasable on eBay for under $15).  Please note that copying a CD into a digital file is only authorized under certain conditions which depend on your country.

There are plenty of apps for mobile phones/tablets which can accomplish pitch and tempo alterations, but they vary in quality, features, and price (the Amazing Slow Downer is an excellent paid app, available for both Apple and Android).  If you want one free solution that will cover it all, CAMco recommends Audacity, a completely free, open-source audio software that can tweak audio in seconds on a computer (for Mac, PC, or Linux users).  After installing and opening the software, simply follow the steps below.  

Pitch

Some countries establish a higher tuning pitch for "A," like 443 Hz (as opposed to the the USA standard of A=440 Hz).  Fortunately, it is very easy to adjust the pitch of an audio file to fit any tuning standard, without altering the tempo.

1. Drag and drop an audio file into the empty work area
2. From the top toolbar, select "Effect" > "Change Pitch..."
3. Input the desired changes, and click "OK"
4. Save the new file, and you're done!

example: To change an A=443 audio file to A=440, simply input those values in the "Frequency" section of the window.

This tool can also be used to change the key of a piece, which could be useful if you want to transpose an audio track from a different instrument (ex: violin, which is tuned a whole-step higher than the B♭ soprano clarinet).  In this case, use the "Pitch" section of the window; select the current key, and the new key.

Tempo

Some audio products offer accompanying tools to control the playback speed, or are produced with a few different speed options to choose from.   If you would like to slow down a particular audio file which lacks these options, then Audacity can also provide the solution:

1. Drag and drop an audio file into the empty work area
2. From the top toolbar, select "Effect" > "Change Tempo..." 
3. Input the current tempo and the newly desired tempo, and click "OK"
4. Save the new file, and you're done!

If the product doesn't indicate the current tempo, then you can determine it with a metronome, or simply input a "dummy" current tempo value of 120, and drag the slider slightly in the desired direction.  You may also select "Preview" in this window to hear the result, and adjust the settings if needed.