You can change the size of the font from 50% to 150% using the dropdown menu. Changing the font size will affect all fonts within your water fall chart diagram.
If you enable the headers under the "Format" tab, you can display the names of dimensions used in your Sankey Diagrams. Once enabled, you can use header aliases to change the names of dimensions displayed above the Sankey Nodes.
Part of the Waterfall chart configuration panel -> Labels
