The limit of $6,000 is for taking new money from outside the Roth, and putting it inside the Roth. When you switch investments within the Roth, the IRS doesn't care (*). Also for a Roth where you've contributed $6,000, you can remove $6,000 without any tax impact. It's the growth of that money that has tax implications if you withdraw it before age 59.5.
(*) except if you sell something at a loss elsewhere, and buy it in your Roth - a "wash sale"