Changing Comment Display/Template

Just been having a hard time with figuring this out so I thought I might post about it (though I usually end up figuring out the answer myself before I get any replies..)

I’m trying to change how my comments look like
(here’s a sample: https://mitomeru.net/?p=258#comment-23 ).

As you can see, comments are displayed with Avatar to the left and the author/date underneath the avatar (with the actual comment body to the right). I was wondering where I should go to edit how this appear (ie. so that the author name/date/time appears beside the avatar and the actual content appears below the above.

Should I go poking around in the CSS or rather commentlist or comments.php? (To make it more confusing my theme also has a “basic-comments.php” and a “old-comments.php” for which I can only guess which each is used for). I believe it would be CSS.. but I’m still having a bit of trouble figuring that out xD.

Anyways, any help is appreciated, just point me in the right direction and I can probably figure out the rest on my own.