If you want change the template, copy your template of certificate in the img directory.
Make sure you name it Template.jpeg if you don't then you have to change im = Image.open(r'Template.jpg') to im = Image.open(r'name of your template with extension')
If you want change the fonts, copy your fonts in the Fonts directory. You can Downlaod your front here
Which font do you change if you want to change font used for attendees name you should change fon = ImageFont.truetype("GothamBold.ttf", 60) to fon = ImageFont.truetype("font you want to use", size of font)
And if you want to change font used for Signatures you should change fox = ImageFont.truetype("PWSignaturetwo.ttf", 50) to fox = ImageFont.truetype("font you want to use", size of font)