You can alter the style of a calendar by applying a new smart grid. Click on the tab marked grids along the left side of the editor (see below). This will display a selection of different grid styles. Simply scroll through the list until you find the one you like. You can then click and drag this new grid onto your calendar.
Once you drop the new grid over the existing one, you'll be prompted with the panel shown below. It will give you the option to replace only that grid, or all of them. The grids you choose to be replace will have the new ones inserted into the same space.