how to disable Sidebar ?

[Connie]

Sagheer,

first you have to tell us which theme you use
then we can tell you which part of the template you have to delete (and which CSS should be changed maybe)

but the best would be that you check the list of themes in the theme repository, http://get-simple.info/extend/all_themes.php

if you are new to all of this the best suggestion would be to use a theme without sidebar from the beginning