Problems deleting an address

I need your help.
In my Yahoo mailbox, I receive spam I cannot avoid. One day, I clicked on an address, and it was stored in the bar addresses, and the historial record. I tried to delete from both, but is not possible. At the historial register, Ican erase succesfully any other direction I want, but when I mark the undesired address to delete it, the program can’t do this.
How can I erase definitively from the historial and the address bar the directions?