Dex Cool

I have a 2000 Grand Am SE and afaik the coolant has never been flushed out and changed. I've had it since 2004. It now has 141k on it. I haven't had any issues out of it till this spring. The temp gauge always stayed at 200 and now when idling it creeps a little past it. I got to looking and the coolant looks a little dirty. I know its a over due for a change because it states 150k or 5 years. Its been over 2 years. I've also recently read one should change it about every 2-3 years.

I am gonna have it flushed and changed within a week. Is this likely the reason for the engine to run a littler hotter while idling? What would be the proper way to flush it and refill it?

It won't hurt anything to flush and refill. I would replace the Dex with Prestone Extended Life antifreeze and you might want to change the thermostat while you are at it. Also make sure your fans are coming on at the correct time since you say the temp increases at idle.