Though it is possible to delete the existing field and create a new one with same name and different type, if it's possible to change it's type directly it would be great.

I understand that it needs to check the existing connections.

If, there is no connection

Simple to change the field type

If, there are connections

Great if data can be transferred to new field type.

E.g.

Single/Multiline line, as a Paragraph, to Rich text

Image, inserted as img, to Rich text

Dropdown, as a list, to Rich text

And likewise for the related or possible fields where it makes sense.

If not, prompt to delete or view the connections and then allow to switch.