Removing knobs to replace ignitor?

My Tappen stove it about 30 years old and works great, but I need to replace 2 of the switch ignitors. I have ordered them but I cannot remove the knobs on the stove front to get to the ignitor. I can’t beleive that in 30 years I heve never romoved these knobs to clean them! Is there a trick to removing them or am I just being to gentle with them?

Thank you
Terry