Go to Structure --> Content Types --> <your-content-type> --> Manage Display
If the Layout option says 'None', change it to 'One Column' under 'Display Suite' and save it.
Now, click on the 'Gear' like settings icon corresponding to the field you want to customize. On the next screen, change the "Choose a Field Template" to "Expert".
Now, click on the 'Outer wrapper' check box and in the corresponding 'Element' field type is either p or div based on your need. If you choose div, then type in biggerfont in the corresponding 'Classes' field. Click on Update and then click on the Save button.'