Sorry, I explained myself badly. After pasting the command on the prompt and hitting enter, the windows Update Standalone Installer showed, asking if I wanted to uninstall the update KB3149090 and I hit Yes. Then the uninstall process started and proceeded until the progress bar was full. The only thing that not appeared was a dialog box to confirm "Uninstall successful". However, I think the update was correctly uninstalled: in fact, if I retry to type and uninstall it, now it says "the update KB3149090 is not installed"