you do not have to cut the serger part just cut the thread by using seam ripper. cut the looper threads and i don't remember if it the front or back and pull the thread then use seam ripper and cut the straight stitch .
If it is a 3 threader you will have 2 loopers and one straight , but a 4 threader it is 2 loopers and 2 straight
I use to sew and that is how i did mine when i had to remove my thread