Change field type from "text field" to "integer" I have a field that is numerical in nature and it was setup as text field. The problem is that sorting by ascending, the number 111 comes before 20.
One option could be to create another field, of integer format. 

Then using PHPMyAdmin (or similar) copy the contents of the  field_data_field_FIELDNAME_TEXT_FIELD into your newly created field_data_field_FIELDNAME_INTEGER_FIELD. 

If that works you can then delete the original text field.