Removing old custom fields

Hi everyone,

I have three old custom fields I want to remove via my SQL admin panel.

Those were three custom fields for
– a featured post image,
– a thumbnail image for the post and
– a large image for the post.

I used these three fields with an old theme and they are still available as drop-down items in the custom fields section of my post panel.

Because I’m not using images anymore, I would like to remove every reference to these old images (they were links entered into each custom field) by simply deleting the custom fields permanently in my site’s SQL database.

My problem: I don’t know in which table to find them.
Can anyone help?

Thanks for looking!