Warning! When double-clicking any text, a font properties bar should appear - please refrain from using this bar to change the font size as it is not compatible with font sizes in bucket.io, using this bar would only create issues along the way.
Like all properties, Font Size is located at the Properties page identified with the Tools icon
Click to select the area that needs a font size change, this should highlight the container in blue, you can also select a specific part of the text in case you don’t wish to change the font size to the entire section
Click properties and from the left-hand side menu bar, scroll down to the Font Properties section
Locate the Font Size area an apply changes