How do I switch to a new insurance carrier?
Your best bet is to wait until the next open enrollment, which will be in November and December for start-up in January. But if you need to change sooner, there is a way.
If you got your health insurance from the exchange, then you would go to the exchange, enroll in your new plan, and then un-enroll from your current plan. The system may or may not let you do it in that order, but your goal needs to be to keep your current plan until you are certain you have the new one in place. The new plan may want proof that you have coverage currently; they accept new customers only during open enrollment. Where you are coming from one plan to another, they should accept you in mid-year.
Keep in mind that your subsidies, if you got any, might also change.