The XES standard is used for process mining, find details here https://xes-standard.org/.
The DCR XML Log format is a log format dedicated for declarative process mining.
The main difference between XES and DCR XML Log is that XES is more verbose.
Use our online converter which can be found here.
DCR Solutions provide a XSLT that can convert DCR XML Log into XES. It can be downloaded from this link.
Variout tools exists that can convert xml using a XSLT. An example is the the Free Online XSLT Transformer.
BPI challenges
It seems that the XES files created for the BPI challenges does not follow the XES standard! A snippet is taken from the files below.
<?xml version="1.0" encoding="UTF-8"?>
<!-- XES version 1849.2016 (IEEE 1849-2016) -->
<log xes.version="1849.2016" xmlns="http://www.xes-standard.org" >...
The XSD schema for XES is defined here http://www.xes-standard.org/downloads/xes-ieee-1849-2016.xsd and using that definition for validation (e.g. https://www.freeformatter.com/xml-validator-xsd.html) then we get an error.

Removing the namespace e.g.
xmlns="http:///www.xes-standard.org"
from the XES file solves the problem.