Replace nodes in xml file

I have an xml config file whose nodes are to be replaced into the
source xml file I am transforming using xslt. The source file will be
as

<source>
<element name="abc">
<a>1</a>
<b>2</b>
<c>3</c>
<d>4</d>
</element>
<element name="xyz">
<a>4</a>
<b>3</b>
<c>2</c>
<d>1</d>
</element>
</source>

The config file has nodes defined in this format:

<config>
<element name="abc">
<a>5</a>
<d>9</d>
</element>
<element name="xyz">
<a>5</a>
<d>9</d>
</element>
</config>

I need help in writing xslt to read nodes matching
config/element/@name with source/element/@name and replace nodes in
the source file.

Thanks