I am surprised none of the guys here have mentioned about this. Firstly, I would like to say that no matter how many wipes or formats you do over the hard drive, the data can still be recovered. I have myself recovered wiped data using some tools.

Yes you can swap the hard drive with a new one but that would require you to spend some money to buy a new one.

But no need to worry there is a possible solution to this and that is DBAN the hard drive.
DBAN - Darik's Boot and Nuke is a program to permanently remove a hard disk's data and overwrite it until the data is unrecoverable.

The only drawback is that this program takes hours of time to complete the process.
We are talking somewhere near 24 hours. But it works like a charm.