I have just upgraded to Samsung Z3 and its a nightmare

the screen never stops trying to clean the system, I have dozens of viruses, an overheated processor,  a full memory, all this according to the dozens of Apps that arrived with the phone. So how do i get rid of the Apps, and if i have to keep a couple which ones would be best to keep. ? All I do with the phone is text and call,  and at the moment all I seem to be doing is deleting the app on the screen  and trying to stop them from re appearing in seconds.  Why did Samsung load all this crap on the hard drive anyway.