Section 17

You should look sec. 17, 18 and 19 of the Companies Act for the same. 

The best thing you can do is .... If your co. is pvt. co., hold the EGM again and pass the resolution again and do all the formalities again within time...

If your is a Pub. co. then follow Companies Act, the sections I have mentioned above.

Agree with Shridhi. You have to make an application to CLB for condonation of delay and only when you get CLB orders condoning the delay you can file Form 23 for change in object clause. It's a bit time consuming process.

Alterntively you can adopt the second method if the company has not yet commenced any business covered by the new objects.