If the Gmail application was pre-installed by the carrier, then it's impossible to remove it unless you root the phone. My advice is to enable IMAP and POP on your mobile and configure the Email application on the phone. I can guarantee that Email is working many times better than the default Gmail app where emails remain stuck in the Outbox folder.
You can use XDA Forums to input your phone's model to see how to root the application: http://forum.xda-developers.com/
