You are able to change the size of the text by highlighting the selected text. This will show the white, circle anchors around the selected text. Click one of the anchors using your mouse and stretch it with the mouse to make it smaller or bigger to your liking. You are also able to change the sizes for different words and strings of text by deselecting your current text where the anchors on the outside of the text do not show. Click "add text" on the menu on the right.