Currently I own a lot of altcoin, I bought them at ico. My account is being downgraded several times. There are many people who say bitcoin will continue to decrease, so altcoin prices also decreased compared to USDT. So now, should I sell them and wait for the price to buy back? Give me advice 
You could sell some of your altcoins if they have climb up high or made some profit on them, and then buy back when it falls again. Though I would recommend that you hold your coins if it's has great potential to grow in near future.
