Try this:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<!-- everything not mentioned below (e.g. text, comments, processing instructions) -->
<xsl:template match="node()">
<xsl:value-of select="."/>
</xsl:template>
<!-- attributes -->
<xsl:template match="@*">
<xsl:attribute name="{concat(translate(substring(local-name(), 1, 1),'QWERTYUIOPASDFGHJKLZXCVBNM','qwertyuiopasdfghjklzxcvbnm'), substring(local-name(), 2))}">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:template>
<!-- elements -->
<xsl:template match="*">
<xsl:element name="{concat(translate(substring(local-name(), 1, 1),'QWERTYUIOPASDFGHJKLZXCVBNM','qwertyuiopasdfghjklzxcvbnm'), substring(local-name(), 2))}">
<xsl:apply-templates select="@* | node()"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
NB: if using XSLT 2 you could replace the translate
function with the lower-case
function.