Assuming you have split your content into 2 or 3 columns and you want to re-arrange the order of the way the content appears. Maybe you want a menu to go on the left side, or on the right?
Assuming you want to move the WP Custom Menu content from the right column into the middle one.
Point your mouse on the WP Custom Menu item until the green popup menu appears. POINT your mouse on the bit that says WP Custom Menu (this can also say something different, depending on the content in your column). Your mouse will change into a 4-arrow mouse. Hold the mouse down and drag it into the column you want it to appear in. Then let go of the mouse.
You can also drag it into a column that already has something in it. Simply drag it above or below the existing content item and it will appear above or below.