Help with updating XML files

I have about 4 to 5 xml small sized xml files (each with say 20 element nodes). I need an way to update the nodes in the XML files from a C++ program. The C++ program would call a function with the right parameters and the right node would be updated (see example below). I am using this in a linux based embedded application and would like to avoid installing an XML database.
 
Example: See the XML file below -
......................
<Sensors>
    <Temperature> 70 </Temperature>
    <Pressure> 200 </Pressure>
    <Humidity> 20 </Humidity>
</Sensors>
...........................
 
How can I update the value of (say) Temperature from 70 to 90 in the XML file from a C++ program?
 
Any help or pointers would be deeply appreciated.
 
Regards,
--Ashish