How do I access the registration information of my form?

It appears that 4 submissions have paid but I do not see their information: name etc...

The submissions may have ended up under the incomplete payments section, you may find them following this guide: https://www.jotform.com/help/135-How-to-View-Incomplete-Payments 

Since you're using PayPal on your form, I would recommend you to enable the IPN option, this way successful payments do not end up marked as incomplete, this guide will help you doing so: https://www.jotform.com/help/276-How-to-Enable-IPN-on-your-Paypal-Account 

I hope this helps.