Modifications are your responsibility to maintain! The following is in theory and has not been tested. Always be sure to update your theme to the latest version before editing template files.
Step 1: Hide the Sidebar
Go to and add the following style to the Custom CSS box:
#archives-page #right-column{display: none;}
#archives-page #left-column{width: 100%;}
Click Save Changes
Step 2: Add a 3rd column
Add the following below the other styles
.archives_list li:nth-child(3n+3) {
margin-right: 0;
}
.archives_list li:nth-child(3n+4) {
clear: left;
}
.archives_list li:nth-child(2n+2) {
margin-left: 20px;
}
.archives_list li:nth-child(2n+3) {
clear: none;
}
Click Save Changes