Don’t know whether this has already been covered.

So many downloads are infested now with this junk, usually advertisement browsers that hijack your default browser. It is possible to delete most but not all.
If Google is your browser go to the three little bars top left on your screen and click, on the scroll down click tools then extensions remove every extension except Google that usually clears the problem though it doesn’t remove the files from your PC. To do that means entering the registry which I wouldn’t advise unless you are competent in that practise.

PS
After deleting extensions make sure Google is ticked as your default browser and check your home page in internet options and restart your PC.