If a pre-14.10 version of TTU is installed then please use the uninstall vb script to uninstall before installing 17.20. See Uninstall Teradata Tools and Utilities Pre-14.10 for details.
Any pre-15.10.10 version of TTU must be uninstalled before installing 17.20. See Uninstalling Teradata Tools and Utilities 14.10 and Later for details.
If a 15.10.10 or later release is installed on the system, then 17.20 can also be installed on the same system without uninstalling the 15.10.10 or later release. See Multi-Version Support for details.
If you need to reinstall 17.20, you must use Programs and Features to uninstall the existing product instance. For more information, see Interactively Uninstalling Teradata Tools and Utilities.