I have delta as my default home page. I did not do this but it automatically did it. So when I try to change it it doesn't change.Delta is causing pop-up adds and disturbing images and articles to pop up.
Use this tutorial to make google as your homepage permanently .
Hope that will help you , and also do an adware cleaner too just in case.
The best way to prevent any program from changing the home page is to lock the browser.startup.homepage pref via a mozilla.cfg file in the Firefox program folder
These functions can be used in the mozilla.cfg file:
defaultPref(); // set new default value
pref(); // set pref, but allow changes in current session
lockPref(); // lock pref, disallow changes
It depends on the browser you are using. Fortunately for you there is a detailed step by step tutorial here for all browsers: http://a-zblogger.com/make-google-my-homepage/