Delete a prefab mesh

Newbie here,

trying to delete a mesh from Prefab but it seems not working as expected:

I have a “Sausage Factory” Prefab and i’m tryin to delete it’s “ambient_occlusion_plane” mesh.

Delete and apply but mesh keep shown in Project as Prefab child.

What i’m doing wrong?

Thanks for your time!

Unity version: 2018.3.0f2

Drag prefab into scene.

Delete Mesh on GameObject.

Drag gameObject with deleted mesh onto prefab in project folder, save over old prefab.

The Hierarchy window is a instantiated (copy) of the prefab. Not the master version that is in the project folder.