Twenty Ten – Move sidebar to left

I’ve solved this myself.

In Dashboard go to
Appearance
Customize
Additional CSS

Enter in box:

/*
LAYOUT: Two columns
DESCRIPTION: Two-column fixed layout with one sidebar right of content
*/

#container {
float: right;
margin: 0 -240px 0 0;
width: 100%;
}
#content {
margin: 0 280px 0 20px;
}
#primary,
#secondary {
float: left;
overflow: hidden;
width: 220px;
}
#secondary {
clear: left;
}
#footer {
clear: both;
width: 100%;
}