Deleting the contents of a cell doesn't usually affect the underlying formatting, so you should be able to clear the data by simply selecting the appropriate cells and pressing the <Delete> button on your keyboard.
If you're having trouble selecting all of the cells in a range, you might try using the <Ctrl>+<Shift>+<Down Arrow> shortcut key combination, which will select all cells that contain data below the current cell. You can also do the same thing using the other arrow keys on your keyboard to select data to the left, right and above the currently selected cell.
If you are using defined tables you shouldn't need to worry about formatting, as the table will automatically apply formatting as data is added. You should, however, be sure to keep at least one row in your table in order to preserve any formulas that you have defined.
You can see more about selecting cells in: Essential Skills Session 2: Doing Useful Work with Excel (Lesson 2-4: Select a range of cells and understand Smart Tags).
If this is a workbook that you use often, you might want to save it as a template to make it easier to create multiple copies of it in the future. You can see how to create templates in: Essential Skills Session 3: Taking Your Skills To The Next Level (Lesson 3-15: Create a template).
I hope this helps, but please feel free to reply if you need any more help with this.
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