Hi,
If you want to access the source code of the .Net project, double click on the .sln file.
You will find .sln file if you extract files from .xsn.
If you are using jscript:
Open InfoPath Go to tool menu, select programming, and select Microsoft script editor and change the code according to you need.
For Web service please look at this link
http://www.w3schools.com/webservices/default.asp
Thanks.