Why my eraser acts weird in illustrator and I can not change my brush color?

[RickyLow]

Hi, I'm new at Illustrator but have been playing for some days with it so I feel comfort using it. Although latley I have had one problem which I'm unable to fix. I have this circle here and everytime I decide to "erase" it becomes like a brush.

This is what I'm talking about:

Does anyone have any idea why and how can I fix this please? Also I'm unable to change brush color...

Thanks for your time.

[Mohammad.Harb]

as a quick answer for you question,  select the object then go to  Object -> Expand appearance 

[marliton]

Hi. If "erase it" means remove it, select it and press Delete or Backspace. You'll need to select it before.

[Monika Gause]

How do you expect the result to look like?

The eraser works like mill-cutting a shape.