When getting Calendar items, use ddwrt:FormatDate to format Date/Time as your liking:

from <xsl:value-of select="ddwrt:FormatDate(string(@EventDate),2057,3)"/>
to <xsl:value-of select="ddwrt:FormatDate(string(@EndDate),2057,3)"/>

Also, you can use custom formatting with this:

<xsl:variable name="monthy" select="ddwrt:FormatDateTime(string(pubDate), 1033, 'MMMM')"/>

More Links to help you:

Available locales

Custom date formats

MSDN DateTime custom format

ms:format-date Function

XSLT Date format dd-MMM-yyyy using ddwrt:FormatDateTime

ddwrt FormatDate and FormatDateTime

How to format date value in SharePoint Data View Web Part – xslt