In Step 3 Customize:

On the left-hand side of the page, you will see our Text options, make sure that you select Text.
You will want to click and drag your cursor mouse in the text box, until it is highlighted in blue.
Then select the font style on the left side.
You can search fonts by name or style:

You can also select the arrows at the top to filter through different categories of fonts:

Quick Tip: you can Double-click to highlight one word, or Triple-Click to highlight the whole line:

Once you highlight your text, select your choice of text options: Font Size, Style, Color, Alignment, Bold, Italics, and Underline

If you have multiple Text boxes, you will need to highlight and make changes in each text box. If you cannot grab each box from their layer, go to the right side Layers and select your Text Box.
Note: Not all font styles will allow you to bold or italicize the text. This is how the typographer created these fonts, and we choose to keep them as they were originally and intentionally designed.