Sound Typist lives in the taskbar's system tray in Windows. Depending on your Windows settings, you may be hiding the system tray icons (Right click the taskbar, Taskbar Settings, and Select which icons appear in the taskbar). Make sure Sound Typist's system tray icon is visible if you want to access it, turn it on/off, change the sound/volume.
Right click it to show the popup menu. Click "Quit". To remove it from starting at login, toggle the "Start Sound Typist at Login".
There's no uninstaller, so to delete it manually, you'll need to find where the installer installs it, probably somewhere under "C:\Users\(your user name)\AppData\Local\Apps\2.0\
You an also grab the portable version, place that wherever you want, and turn on/off the start at login through that.