<xsl:template match="*[local-name() = 'RICHIESTA_PRESTAZIONI_EROGABILI']">
 <ser:ELENCO_PRESTAZIONI xmlns:ser="http://regione.campania.it/schemas/cup">
   <xsl:copy-of select="@*[not(local-name() = 'idCup')]" />
   <xsl:attribute name="idCUP"><xsl:value-of select="@idCup"/></xsl:attribute>
   <ser:PRESTAZIONE />
   <xsl:apply-templates />
 </ser:ELENCO_PRESTAZIONI>
</xsl:template>

--
Regards,
Mukul Gandhi