To remove the unwanted icons on the home screen, tap and hold the unwanted app icon. A delete option should appear. Drag the icon to the delete option and it should be removed from the home screen. This will not delete the app from the phone.
Not certain if you can alter the size of the icons. Try tap and holding an empty area on the home screen and see if there is an options menu which allows you to alter the grid size of the screen. If not you may have to get a 3rd party app which allows you to do this. Here is an image of just one of the options available from the Nova Launcher app download As you can see it allows you to alter the size (plus a lot more) of the icons. This is not a recommendation, merely an example to show what is available. There are a lot of others that may suit you better. Just search online.
(Click on image to enlarge for better viewing)