Easily adjust your templates column layout via the templates parameters which can be accessed by navigating to Extensions -> Template Manager -> J51_YourTemplate.
From the Side Column Position dropdown simply select the format of your choice. Left places your SideColumn module position to the left, Right placing it to the right.
For a single column layout simply disable all modules in the SideColumn module position.
Custom Page and Column widths
Your side column width can also be customised via the templates parameters. Place the desired width of your side column in pixels in the Side Column Width field. Your content area will automatically contract/expand to fill the remaining available area.