Grid size for Android apps and widgets on the home screen is changed on Nova Launcher. To change Grid size on Nova launcher and set rows & columns size do as follows:
1. Go to Home Screen and hit "Menu Button"
2. Select "Nova Settings"
3. Tap "Desktop"
4. Tap "Desktop Grid" to change row and column size for your phone's desktop
See:
How to Hide Dock on Nova Launcher
How to Hide Notification Bar on Nova Launcher