Once the chart has been created online, you cannot change the way that the chart looks. What you can do is to create another chart, this time making the desired changes.
Don’t worry- there is no limit on the number of charts that you can create on your site.
If you have generated a chart in Family Tree Builder software, you can edit the chart when it’s displayed on your screen in Family Tree Builder, before you save it as a PDF file.
Please read more information about editing your chart here: How do I create a chart of my family tree in Family Tree Builder software?