Character conversion in stylesheet

Hello,
I have to check if I have some of the extended ASCII (UTF8) characters in the 
input XML file.
So, I am using stylesheet for transformation XML input file to the different 
format of the XML file.
Can I do something efficient to check for special characters in some of the 
fields in the input XML file and to convert those specific characters, (for 
example, è to e) in the output file?


Thank you, 
abelkin