EA app is the new Download Manager for all EA games that will replace Origin soonish. The most important general questions can be found here: [EA app] FAQ.
There’s a few things still missing in EA app and to use these you will need to continue to use Origin for the time being. You can download Origin here (clicking the links will directly start the download): Mac, PC.
You can have both Origin and EA app installed at the same time but only one can run at any given time. So if you generally want to switch to EA app but keep Origin for the things EA app can’t do yet, that is possible.