I agree to what Timmappa has said and am not repeating the same steps.
Just to ensure you that it is the correct process, I can say, Log In to your online SB account, from the same e-services and SMS alerts you will get a small list of notification tips appearing at the middle bottom of the page saying, know More about SMS alerts. There you get this set of Question and Answer displayed:
"Can I disable all alerts for an account?
Yes. In the SMS Alerts Registration/Updation page, select an account and click the disable hyperlink. SMS alerts will be disabled after getting your confirmation in a subsequent page."
So you can go ahead with disabling the alerts, but even I suggest you to continue with the service as it will give you an extra level of security. Moreover, for OTP transaction too you will need the service as online Payment has become a part and parcel of our life.