>>>Do I uninstall MSE first then install Avast, then sort the voice thing out
Download the setup file for Avast first but don't run it.
http://www.avast.com/en-gb/index
Uninstall MSE (via your Control Panel and Programs & Features, or whatever your version of Windows calls it).
Then run the Avast installation program.
Lastly, disable that annoying voice notification by right-clicking the Avast icon at the bottom-right of your screen, selecting 'Open Avast! User Interface', clicking 'Appearance' and removing the 'Sounds' tick.