You can first contact the service center to see whether they can replace it for you and t he cost. If you cannot accept the price, you can easily get the new replacement display for the galaxy nexus via international shipping. But carefully to get the part from eBay, because there are many fake parts instead of the original ones.
Hi praveen, if the LCD screen still works, you only have to replace the glass lens, which is much cheaper. But it's also very difficult to replace the glass only if you have no skills of repairing phone. You can read the steps that other users posted above.
It seems you have to replace the whole display assembly, which is about $200. Hope you could afford it. After googled, you can find the new part from Amazon or other online store. But please make sure the new screen is original before purchasing.
You'd better consider what Valiera mentioned above. It's easy to break the glass lens when separating it from the display. You'd better replace the whole screen, which is about $90 rather than $200 that Valiera said. Display assembly repair guides: iPhone 5 LCDとデジタイザの交換
It seems the only way to fix the cracked screen is to replace the screen. If you don't want to waste money, you can just replace the digitizer touch screen rather than the whole screen. But it's not easy to replace the digitizer alone if you don't have any repair skills. You'd better ask help from professional.