def update(self, key=values.unset, value=values.unset):
data = values.of({'<STR_LIT>': key, '<STR_LIT>': value, })<EOL>payload = self._version.update(<EOL>'<STR_LIT:POST>',<EOL>self._uri,<EOL>data=data,<EOL>)<EOL>return VariableInstance(<EOL>self._version,<EOL>payload,<EOL>service_sid=self._solution['<STR_LIT>'],<EOL>environment_sid=self._solution['<STR_LIT>'],<EOL>sid=self._solution['<STR_LIT>'],<EOL>)<EOL>
Update the VariableInstance

:param unicode key: The key
:param unicode value: The value

:returns: Updated VariableInstance
:rtype: twilio.rest.serverless.v1.service.environment.variable.VariableInstance