You can add some extra interest to the text elements of your slides by using the Word art tool in Presentations.
Having selected the slide you want to edit, use Insert > Word Art:
A dialog will open where you can add the text you want to use:
If you want to add multiple lines of text, use Shift + Enter wherever you need to create a line return. When you’re done, press Enter to save.
You can then select the new text box and use the toolbar tools to change the colours, text sizes, fonts and alignment of your word art. (You’ll note that there’s no selector for font size – to change the size of your text, click and drag the handles of the bounding box).
You can even rotate your text in 90 degree increments, if you want to:
For finer control over rotation, drag the round handle above the text box:
Once you’re happy with your word art, click outside the text box and your slide will be auto-saved: