You can remove all settings from all tabs in the Web Service Manager by selecting File > New.
To completely revert to a clean, post-installation state, you can delete the default configuration file. The file is located in:
C:\Users\username\AppData\Local\Trillium_Software\WSDL_UI.exe_zz
\nn\user.config
where nn is the product version number. Delete the nn directory (the whole directory, not just the user.config file) to revert to a clean state.