locked icon

[willow_diamond]

Hi everyone, I know this has probably been asked before, but I looked and couldn't find the answer, and the tutorial linked really confuses me (sorry, I'm a noob, to both coding and smooth sailing). I just want to change my 'locked' security icon. I've tried several things and it's not working, and I'm just confusing myself more and more.

I'm using this code.

any help would be greatly appreciated!