Do you mean that you want both sidebars on the same side (left), or you just want to adjust the setting of the sidebar so it is moved over to the left a little more?
It simple mean if left sidebar does not exist and i want to move right bar (already exist) to left side then how to do
CSS will only adjust dimensions, and colors. If you want to move the entire sidebar you need to edit the function of the way the blog is set up (index.php), which could break the blog if you don't know what you are doing, and even if you do, there is no guarantee that it will work on your theme. The first suggestion would be to just put everything from the right sidebar in the left sidebar, but i have to assume they are different sizes or you would have done that already.... ....so you could adjust the dimensions...make the right sidebar the size of what the left sidebar is now , and make the left sidebar the the size of what the right sidebar is now.(and switch the content). That will keep the dimension of your blog the same, and give your sidebars the opposite functionality of what they have now, This is of course assuming that your side bars start, and end at the same symmetrical points, and are positioned directly opposite of each other, and both have widgets and don't have any other functions coded into the sidebars. . You do that through your CSS file. So IOW if Left sidebar is 160 px wide, and right sidebar is 300px wide.....make the left sidebar 300px wide, and the right sidebar 160px wide.. That's what I would try first, since it seems to be the easiest way, but make sure you have the original files handy in case the theme won't handle those changes and you get a error message. This is hard to say without seeing the blog, since all themes are different, and not knowing what else is coded into the sidebars like subscription functions, ad boxes, popular article plug ins and so one. ...or I would switch the file names Change right sidebar.php renamed to left sidebar.php, and left sidebar.php, renamed to right sidebar.php.
Yeah, that really what I would do..I do a lot of theme hacking, just about every one I get, and even I don't mess around with completely changing the sidebar locations, I'll just get another theme. Too much can go wrong if you are not versed in PHP, and if you are , you can build one that does what you want.