Purchase or download a digital audio workstation such as Logic Studio or Record (see Resources). These software applications allow you to quickly convert sampling rates of audio in a variety of file types.
Launch the software package and import your audio file. You can usually accomplish this by selecting "Import Audio" from the "File" menu. Refer to the documentation provided with your software if you're unfamiliar with these processes.
Change the sample rate of the designated audio file by selecting "Bounce" or "Export Audio File" from the "File" menu and selecting the desired 44.1 Khz sample rate from the dialog that appears. The saved audio file will now utilize the new sampling rate.