|Assuming you are using IE then all you should have to do is go to the website then in IE > Tools > Internet Options > General tab and hit the "Use default" button.|
If that's what you are doing and it won't stick then two possibilities come to mind:
1. You have some protection software onboard which is stopping your home page from being hijacked.
2. You have some sort of infection. In this case first step would be to download MalwareBytes freebie from here:
Install it, update it and run it. Let it fix all it finds.
Always pop back and let us know the outcome - thanks