There is no way to adjust the leading or paragraph spacing in a Premiere Elements title. But you can fudge it in a couple of ways:
1) Add a line of blank text between two lines of text. It need only include a couple of spacebar spaces. Then select that blank text line and change its font size to whatever size you need to give you the proper spacing. Or
2) Just create a separate text box on your title by clicking with the text tool. A title can include as many blocks of text as you'd like. Drag and position them as near or as far from each other as you need.