Bellow are the code lines I used in my child theme for removing the left sidebar. I strongly recommend to have a child theme for making this changes.
My new space is 620px instead of 470px. Where you see this number 65.95744680851064%, is the operation of 620/940. 940px is the full width of the theme. This mean that if your new desired space is 700px, you have to put the number given by 700/940.
.content-wrap {
float: left;
width: 100%;
}
.featured-wrapper {
float: left;
width: 65.95744680851064%; /* 620 / 940 = 0.6595744680851064 */
}
.aside {
float: right;
}
#content {
float: left;
width: 65.95744680851064%; /* 620 / 940 = 0.6595744680851064 */
}
Maybe you will encounter some problems after changing your theme to 2 columns (like post thumbnail remaining at old size, etc.). You can resolve that problems also.
Try this lines above, and let know if it worked.