Modifying the field type
For some free fields you can modify the field type. If the field type cannot be modified, the Field type field is grayed out.
Warning  
When modifying the field type, all field information that was entered previously will be lost. Make sure to check beforehand if the field contains any information that should not be deleted.
Procedure
1. Go to Field definer > Business objects.
2. Select the relevant business object and set its status to Under construction.
3. Go to Details > Fields.
4. Select the field for which you want to change the type and ensure its In use attribute is set to Yes.
5. Go to the Field type field and click on the picklist button.
A dialog box is displayed containing the possible field types.
6. Select the required field type.
7. Save your settings.
8. Set the business object’s status back to Completed.