Is it possible to change a field name in ArcGIS Online or Portal for ArcGIS?

Answer

No, it is not possible to change a field name in ArcGIS Online or Portal for ArcGIS. Once a field name is set and saved in its source layer, it cannot be changed. However, the display name of the field name can be changed in ArcGIS Online or Portal for ArcGIS. A display name is the field name displayed on the hosted feature layer's attribute table. Refer to ArcGIS Online: Set a display name or Portal for ArcGIS: Set a display name for more information and instructions to change a field's display name.

Alternatively, if a new name is required to ensure data precision, add a new field and copy the field values from the intended field to the new field by following the steps provided below.

1. Log in to Portal for ArcGIS or ArcGIS Online.
2. Click Content > My content.
3. Navigate to and click the feature layer to open its item details page.
4. On the item details page, click Data > Table.
5. Add a new field in the attribute table.
   1. In the attribute table view, click the Options button and select Add Field.
   2. In the Add Field window, specify the parameters and click Add New Field.
6. Copy the intended field value to the newly created field.
   1. Click the newly created field column header and select Calculate.
   2. In the Calculate Field : <field name> window, click SQL.
   3. In the Calculate Field window, under Fields, select the field with the values to be copied from.
   4. Click the Validate button to validate the expression.
   5. Click Calculate.