You can change the height of the rows with the mouse or through the dialog.
What is described here for rows and row height applies accordingly for columns and column width.
Using the mouse to change the row height or column width
Click the area of the headers on the separator below the current row, keep the mouse button pressed and drag up or down in order to change the row height.
Select the optimal row height by double-clicking the separator below the row.
Using the dialog to change the row height or column width
Click the row so that you achieve the focus.
Start the context menu on the header at the left-hand side.
You will see the commands Height and Optimal row height. Choosing either opens a dialog.