1. Assuming you mean Avast (antivirus) instead of Advast, it's a setting in that program, not in Windows. https://www.google.com/search?q=avast+email+signature tells all you need to know.
2. That depends on the browser you're using. I assume you tried in Edge and in Internet Explorer (you didn't tell what browser you use). Just in case you didn't: https://www.google.com/search?q=edge+default+search+engine tells how to do it.
And, of course, Firefox and Chrome (both free) support it. They run fine in Windows 10.
Removing Advast in email & need google search
BY CaliNanni | JANUARY 8, 2019 12:32 PM PST
I'm having a difficult time with the following issues.
1. Can't delete the Advast Signature off of my email.
2. Can't delete Bing and insert Google Search instead.