registration as new tax payer or conversion from existing tax based registration?

Hello everyone
I am registered service tax payer and I am not not even converted to gst. Now I want to know whether I need to convert to gst or else I can stay in existing service tax
If I need to change to gst how it could be done ie., by conversion or new registration as
The due date given by government expires, whether it effects my registration process

Please anyone help me regarding this