Unfortunately, there really is not an easy way to do this, the only thing that I can do is to tell you what I would do given the same scenario.
1) I would not delete the repeater
2) I would create the new fields
3) I would create a filter (https://www.advancedcustomfields.com/resources/acf-load_value/) that runs when the value is loaded for the new fields. If the new field does not have a value (has never been set) then retrieve the corresponding value from the old field. This will work to automatically transfer the old values to the new field when a post is edited.
4) I would create and action (https://www.advancedcustomfields.com/resources/acf-save_post/). In this action I would delete the old fields from each post as it is updated using the new fields.
5) With #3 & #4 in place and working successfully I would create another filter (https://www.advancedcustomfields.com/resources/acf-prepare_field/) for the repeater to hide the old field (return false). This leaves the old fields and data in place and sill retrievable for #3 and for #6 (coming up)
6) Alter the template file(s) where the old values are used. First see if the new field has a value and if it does use the new field. If the new field does not have a value then to get the value from the old field and use it.
