To uninstall TrueCrypt on Windows XP, select Start menu > Settings > Control
Panel > Add or Remove Programs > TrueCrypt > Change/Remove.
TrueCrypt on Windows Vista or later, select Start menu > Computer >
Uninstall or change a program > TrueCrypt > Uninstall.
No TrueCrypt volume will be removed when you uninstall TrueCrypt. You will be able to mount your TrueCrypt volume(s) again after you install TrueCrypt or when you run it in portable mode.
See also: How to Remove Encryption