What the others said about hitting the Tab key and shift+Tab, and also...
You have to hit the Tab or Shift+Tab at the beginning of the bullet -- when
your cursor is between the bullet and the text, otherwise hitting Tab just
adds a tab to the text.
There are also icons on the Formatting toolbar you can use with your cursor
anywhere in the line. They're called Increase Indent and Decrease Indent.
You'll see the tooltip with that label if you hover your mouse over the
icons on the Formatting toolbar. (The icons look a little like an arrow
pointing either to or away from a horizontal bar chart.)