How can I swap/transpose the rows and columns of (Excel) data?

You can easily change the row or column order in your Excel spreadsheet by clicking Edit Data in the function bar.   

This opens the window of your Excel table, where you can use the options in the section Table to change the order of the data or to swap rows and columns.

You can also set the serial order in reverse under Data or change the waterfall direction, as in this example.