The S & P 500 is up nearly 8% so far this year, and there are signs that certain sectors and stocks are overbought. Big Tech in particular is nearing or at new highs and dominating indexes . In the first quarter, most gains came from just a few mega-cap stocks in the S & P 500 . Now's a good time to be making some changes to your portfolio, Dave Sekera, chief U.S. market strategist at Morningstar, told CNBC's " Squawk Box Asia " on Wednesday.
One of them is Alphabet , which is already up 37% this year. "Alphabet has had a great run," he said. "It's still a four-star-rated stock [and it] trades at almost a 20% discount." According to FactSet, analysts give the stock average potential upside of 8%.