To change line spacing, select a text element in question and click Edit text to find out its font type and size (heading or paragraph, e.g. Paragraph 2).
Then, go to Styles > Text > Edit text styles > select Paragraph or Heading depending on your text element > find a particular font and change the Line height.
Also, you can use the following keyboard buttons for starting a new paragraph and a new line:
Use Enter for a new paragraph
Use Shift+Enter (Windows) or Command+Enter (Mac) for a new line