Simply check out the Apple website and enter your serial number to see if your iMac's hard drive can be upgraded for free.
Apple may replace your hard drive free of charge…
If you bought an Apple iMac product between December 2012 and September 2013, Apple or and Authorised Service Provider may replace your hard disk drive free of charge. All you need to do is visit their website and type in the serial number of your product to see if it’s effected.
Apple relies on quality hard drives to power their products and where there may be data recovery issues, they are always quick to help. Hard disk drive manufacturers do unwittingly release drives with bugs – more often than not relating to firmware codes. Although it is rare, this does happen and sometimes products can be recalled.
Before getting your product serviced, make sure you back up all of your data. Once a hard drive is replaced you may need to reinstall the operating system and any data. To find the serial number of your iMac check the OS X, base of the computer or the product packaging if you still have it. Users should note that this program only covers iMac models three years of their original date of sale
Reference: http://www.datarecoveryspecialists.co.uk/blog/apple-may-replace-your-hard-drive-free-of-charge
