You don't need to shorten the chain, unless you want to save a few grams. Otherwise you're better off leaving it as it to preserve its integrity.

You will want to drop the FD to keep it close to the new outer ring in order to maintain crisp shifting.

Now the hard part......
Index outer chainrings have pickup pins and shift gates phased to the inner ring. If your new 50t is not Shimano and/or made to pair with the 36t you MIGHT lose some shift smoothness. Even so it should still be OK.