I have that very serger. I don't change the threads all that often because for the pajama pants I have been making, it doesn't really matter. But, I did take a class where I bought it and she had us take all the threads out and rethread. I don't know if I remember, but, I was able to do it. I would now just tie the new threads to the old ones if possible. I don't use it for half of what it can do, but, I'd wanted one for a long time and for what I have used it, I'm very pleased.