You donít have to remove the thermostat, there is always a bypass to a thermostat, Although it can be very low flow.
Drain your coolant first for disposal, then turn on the hose, wait for water to flow out of the overflow and wait until it is nothing but clean pure water.
I crank the engine at this time and let it idle so water flow is established throughout the engine and run until itís clear, clean water.
I have removed a thermostat before on a nasty engine, but donít think you have to.
Following the instructions provided with the flush kit seems to work.
Just of course our water heater hose is the normal car heater hose, so you donít have to turn the heater to full