To change your AOL sounds (and any other sounds on your computer) you use the Windows Control Panel. Click on the 'Start' button in the bottom left-hand corner of your screen, select 'Settings' and then 'Control Panel'. Double-click on the 'Sounds' icon and the 'Sounds Properties' window will appear. This contains a list of all the events that have a sounds assigned to them. (If you scroll down to the bottom of the list you will find the AOL sounds.) Click to highlight the event you wish assign a new sound to, then click the 'Browse' button. Search through your folders until you find the new sound, highlight it and then click 'Ok'. Repeat this for all the sounds you wish to change, then click 'Apply' followed by 'OK'.
NOTE: The sounds have to be WAV files. MP3 or other formats will not work.