If you wish to change the default text in WordPress from Paragraph to either italic or preformatted just go to the box with paragraph on it paragraph

Click on it and move it to which ever format you want. paragraph opened.

You can also change the text format for  part of your post. Just highlight the words you want changed, again click on the paragraph box and click on which format you want. The words should change. Note the words in the paragraph will change, not just one word.

To get one word only to change,  to italic, highlight the word and click on the italic symbol. italic symbol The word will then change.