Adjusting banner ad size

I have successfully implemented ads, but I cannot manage to find anything about setting the size of banners. My current code that I have used and successfully tried is:

 public class BannerAdScript : MonoBehaviour
 {
 
     public string gameId = "1234567";
     public string placementId = "bannerPlacement";
     public bool testMode = true;
     [SerializeField] BannerPosition _bannerPosition = BannerPosition.BOTTOM_CENTER;
 
     void Start()
     {
         // Initialize the SDK if you haven't already done so:
         Advertisement.Initialize(gameId, testMode);
         StartCoroutine(ShowBannerWhenReady());
 
         // Set the banner position:
         Advertisement.Banner.SetPosition(_bannerPosition);
     }
 
     IEnumerator ShowBannerWhenReady()
     {
         while (!Advertisement.IsReady(placementId))
         {
             yield return new WaitForSeconds(0.5f);
         }
         Advertisement.Banner.Show(placementId);
     }
 }

How do I set the height in a banner ad?