Copy a field in the database to an other field for ALL rows

I have uploaded a large database and want to change the type of a field from text to number.
As I’m not able to change the type of the database field AND to delete the entire database at once I’m looking for the option to make a loop that copies the text field into a new number field for all my database rows.

is that possible and how?
if not, what are my options?

Thanks a lot for your help!