WP logo in dashboard not changing

Hi,
I am trying to change the icon on the top left of the admin dashboard. I have the two options in plugin's settings, but, when I change the image, I only have new images on the login page and favicon. The logo on the dashboard remains. First I had a square image, and I thought that's why is not changing in admin, but I've also tried with 310px by 70 px, and still have the wp logo. Can you, please, tell me what I did wrong?
Thank you