Call them and tell them that you have been using the card for many months / years and have never defaulted [if you haven't] Ask for review of the Credit Line. One, if you are good customer, they do it without doing any CIBIL inquiry. If you are not then, CIBIL inquiry will be done and after that it will be intimated to you.
Strongly Advise you to go for enhancing credit line only if you are able to pay the bills in Full every month.
