No Sidebar Full Width

If you do not wish to show Side­bar than choose No Side­bar Full Width on the par­tic­u­lar page, just edit the page and choose the No Side­bar Full Width from Select Lay­out Attribute Box on bot­tom right. For a par­tic­u­lar page, if you select the Lay­out in the page than it will over­ride the Lay­out set­ting set from the customize.

If you wish to change the Lay­out of all the pages than go to Appear­ance-> Cus­tomize-> Design Options and choose Default Lay­out For Pages only.