Deleting keys

Hello, I’m totally new to wordpress and I’m also not really proficient in php either so I hope you bear with my questions.

Well my problem is I want to delete a key that says ‘Current Mood:’and I can’t seem to do it. Its just there I’m not using it in any posts. I just want to delete it cause its idle and useless. I’ve read the delete_post_meta page already, but now my problem is where do i put the codes?

I’m sorry if you are little annoyed. I’ve done my best to use google search engines and wordpress docs but i cant seem to have the right key words if there is a topic about it already.

Thanks for help!