yes you can.doing so will,however,erase all data on the drive so if you have anything you want to save,back it up first.just go into your boot menu and select dvd rom as first boot device or usb device if you are installing your os that way.insert media and reboot.you will be taken to an install screen where you will be given install options.select custom or clean install and that is about that.to be more specific we would need to know what os you are overwriting and with what other os you are doing it with.
