Problems changing a drop in...

I have an UltraFire WF-502B and that’s easy to put a different drop in in, but I’ve also got a WF-501B and I can’t even get the old one out of it. I got the big spring out and tore the small one off, but still can’t get the drop in out. I’ve tried unscrewing it but can’t get anywhere with that either. Does anyone have any other suggestion?

Thanks for any help!
David

Front screws off, if it was never greased it may be tough. :)