Has the coolant started to turn more towards yellow / brown rather than green? If the coolant looks greenish I'd do a 1X fill with water then drive for a few miles rinse. Heat does wonders in cleaning things out.

If the coolant is brown, opening the block drain then filling from the tank would be the first step.

A word of caution, if your drain is like mine, it works like a brake bleeder screw. Mine has a thread issue that prohibits opening past 3/4 of a turn. If it is forced past that point I'm concerned that the threads will be torn out.

Just pulling the thermostat on these cars isn't a good idea. The disc on the bottom of the stat is needed to block the bypass when the stat opens.