If a module on the homepage is unlocked, it can be moved the same as any module on an internal page - select the module, grab the handle, and drag it to another position in the same column or into another column.
You cannot move a locked module, or move an unlocked module into a locked column. It's easy to tell if a module is locked; you can't drag it around. If a column is locked, the orange chevron (the big orange angled connecting lines) above will not appear.
If you need a locked module on the homepage moved, you can ask [email protected] for help.