Click "Tools" -> Options -> Display -> and it's the section named "HUD - Tiny: HUD Panel". There you can set the Position where X= Horizontal on your screen and Y= Vertical on your screen. You can't change how it looks like in game but you can change the stream overlay (that only show up using something like OBS). To find that click "Overlay" -> "Streaming Overlay" -> right click the new thing that pops up -> "Overlay Image".

If you want to change the image that pops up whenever you get something like a headshot or killstreak: "Tools" -> Audio -> Configure -> and click the button at the bottom center portion where it shows the standard green pop up that's labelled "...".