Thank you everyone for your reply's .
Finally this worked for me
datasource = AdminConfig.getid('/DataSource:datasourcename')
properties = AdminConfig.list('J2EEResourceProperty', datasource).splitlines()
for prop in properties:
propName = AdminConfig.showAttribute(prop, 'name')
if (propName == "serverName"):
AdminConfig.modify(prop,'[[value newname]]')
AdminConfig.save()