My process is to set up the database / content manager and use the static pages as reference to copy the text from it, and paste it to their respective columns/fields in the content manager.
Once done, THEN and only then delete your static pages by click on the three dots in the page manager to DELETE. This is part is really easy.
IMPORTANT: If the site has history with search engines and visitors, be sure to add a redirect for each page change to a dynamic page, as the URL will now include the collect name
/static-page-url
will change to
/name-of-collection/new-dynamic-page-url