cannot change the type of brush stroke in Illustrator

Hello,

I'm learning to use illustrator and I've made a brush stroke, but I cannot change the type of brush stroke.

This is what I do: I select the stroke I've made, I go to the panel at the top, I change the type of brush stroke but it doesn't work.

Even if I select any type of brush stroke, and I use the brush , the brush stroke is always the same.

(setting of colors and width of the strokes works perfectly)

Which is the problem? How somebody can help me because I'm not able to find a solution.

Thank you!