After placing an artifact of any type, you may decide that this not the right spot in the room. You can easily move it in another spot. In the ‘Curate exhibition room’ overlay, left click on the specific artifact and select the first option that appears to you, which is ‘Move’. Selecting Move, you re-place your artifact in another spot just exactly as you placed it in the first place. That is, move your mouse, navigate with your keyboard keys, find the right height and click, as being described in the Place an artifact help page.