How can I only allow specific file types?

You can control what file types your customers are allowed to upload in the File settings section.

Select "Only allow specific file types". 

Next, you can choose form predefined file types or provide your own by entering file extensions like ".png" or MimeTypes like "image/png". 

After you saved the field config your customers will only be able to upload the file types you provided. 

If you need further assistance, please send us a request and we will be happy to help you out.