Dear Mercime,
I tried it but it seem like I altering the size of the theme instead of the page width. To be clear, i need the page with only a sidebar instead of 2. The current theme template contain 2 sidebars (left & Right).After removing the left sidebar, the post-content aligned to the left together with the right sidebar. In fact, it page and the right sidebar were adjusted automatically into half of the page size. Therefore, i need to resize the page (Post-content width) and turn the right sidebar back to the original size. I hope you can understand what i referring to.