The Ucase request can be used to change all characters in a string field to upper case.
Note: The information in this article applies to only to retired products, ArcView GIS versions 3.x. The instructions described apply to the Avenue programming language, which is specific to the ArcView GIS application. For ArcMap and ArcGIS Pro, this procedure can be done using a Visual Basic or Python expression. In ArcMap or Pro, open the Field Calculator, and click 'About calculating fields' for examples of field calculations. See the article: How To: Convert lower case words to upper case in a string field in ArcGIS Pro