Changing data type for existing metadata

I am trying to edit data type for several of my metadata in order to avoid the "such-and-such field has at least one invalid value!" error messages. More specifically, I want each data type to be "text" rather than "date" or "date range." When I go to edit the item type, I can't find a way to change the data types. Do I have to delete this item type and start from scratch? Could this be a permissions issue?

I would appreciate any help.

I don't think that the data type can be changed. You wouldn't have to delete the item type itself, but it would call for creating new fields on the item type and copying the existing data over into those.

Thanks, @patrickmj. Just for any future readers, I ended up not being able to create new fields with the same metadata names, even after deleting that item type. Omeka had saved that element set and had set its respective data types in stone. SO, I ended up just renaming my metadata and making the relevant changes to items/show.php