Update / Deleting Custom Site Templates

I have created a custom site template in sharepoint online using the modern experience. However, there have been changes made that would impact future sites created with that template. Is there a way i can update the site template to accommodate the changes i have made?

Otherwise, if i delete the site template, will it delete the sites i created using said template? It would work just as well for me if i could delete the template, whilst retaining the sites utilizing it, and create a new template based on the changes I’ve made.

Thanks